HISTORY.txt

v1.7 (XXXX-XX-XX)
=================

- Added a general framework for spherical distribution function as
  well as implementations of a few well-known distribution functions,
  including (a) Hernquist distribution functions that are isotropic,
  have constant anisotropy, or have Osipkov-Merritt type anisotropy;
  (b) an isotropic Plummer profile; (c) the King model (also added as
  a potential as KingPotential). These distribution functions can be
  evaluated and sampled, and their velocity moments can be
  computed. Work started in #432 and continued on from there.

- Added NFWPotential initialization method using rmax and vmax, the
  radius and alue at which the rotation curve peaks; also added rmax
  and vmax methods to NFWPotential to compute these quantities for any
  NFWPotential.

- Added general class SphericalPotential to make defining spherical
  potentials easier (#424).

- Added interpSphericalPotential class to build interpolated versions
  of spherical potentials (#424).

- Added potential functions to compute the zero-velocity curve: zvc
  and zvc_range; the latter computes the range in R over which the
  zero-velocity curve is defined, the former gives the positive z
  position on the zero-velocity curve for a given radius in this
  range.

- Added TriaxialGaussianPotential, the potential of a Gaussian that is
  stratified on triaxial ellipsoids (Emsellem et al. 1994). Useful for
  implementing multi-Gaussian expansions of galactic potentials.

- Added AnyAxisymmetricRazorThinDiskPotential, the potential of an
  arbitrary razor-thin, axisymmetric disk.

- Added AnySphericalPotential, the potential of an arbitrary spherical
  density distribution.

- Added inverse action-angle transformations for the isochrone
  potential (actionAngleIsochroneInverse) and for a one-dimensional
  harmonic oscillator (actionAngleHarmonicInverse; also added the
  [x,v] -> [J,O,a] transformation for the latter,
  actionAngleHarmonic).

- Added Potential.plotSurfaceDensity (potential.plotSurfaceDensities)
  method (function) to plot the surface density of a Potential
  instance (of Potential instance of a list of Potential instances).

- Re-implemented the DoubleExponentialDiskPotential in a simpler and
  more accurate manner, using the double-exponential formula (no
  relation) for integrals of Bessel functions from Ogata 2005. The
  DoubleExponentialDiskPotential is now calculated to ~machine
  precision almost everywhere and there is no longer any switch to a
  Keplerian behavior at large R.

- Made potentials as much as possible numerically stable at r=0 and
  r=numpy.inf (i.e., they don't give NaN). Still a few missing, but
  the majority of potentials are well behaved now.

- Fixed angle calculation for actionAngleIsochrone and
  actionAngleSpherical for non-inclined orbits (which are tricky).

- Replace Quantity parsing through the package as much as possible
  with a set of centralized parsers (#430).

- Renamed galpy.util.bovy_coords to galpy.util.coords,
  galpy.util.bovy_conversion to galpy.util.conversion, and
  galpy.util.bovy_plot to galpy.util.plot (but old 'from galpy.util
  import bovy_X' will keep working for now). Also renamed some other
  internal utility modules in the same way (bovy_symplecticode,
  bovy_quadpack, and bovy_ars; these are not kept
  backwards-compatible).

- Added Python 3.9 support.

v1.6 (2020-04-24)
=================

- Added HomogeneousSpherePotential, the potential of a constant
  density sphere out to some radius R.

- Added DehnenSphericalPotential and DehnenCoreSphericalPotential, the
  general potential from Dehnen (1993) and its cored special case
  (#403).

- Standardized the way packages are imported: numpy as 'import numpy',
  avoid use of math, don't use scipy's numpy interface, internal
  imports for all galpy imports.

- Implemented ChandrasekharDynamicalFrictionForce in C, introducing a
  general scheme for easily implementing velocity-dependent forces in
  C without requiring all forces to take velocity arguments (#420).

- Fixed AMUSE compatibility with Potentials instantiated with physical
  inputs (#405).

- Fix how DiskSCFPotential instances with a hole in the surface
  density get passed to C (was wrong when type == 'exp', but 'Rhole'
  was in the list of parameters, hole was not passed; meant that
  McMillan17 was wrong in C in v1.5).

- Add time dependence to all relevant Potential functions and method
  (#404).

- Raise warning when r < minr (where dynamical friction gets turned
  off) in an orbit integration that includes dynamical friction (to
  avoid silent turning off of the dynamical friction force; #356).

- Improve performance of orbit animations (#414).

- Fixed compilation issue for Intel compilers: no need to include
  'lgomp' in the linking step (#416).

- Compile all main galpy C extensions into a single shared-object
  library libgalpy.

- Automatically build Linux, Mac, and Windows wheels with GitHub
  Actions and upload them to PyPI upon release creation (#421).

v1.5 (2019-09-12)
=================

- Added support for holding multiple objects in an Orbit instance,
  with efficient handling of multiple objects and parallelized
  integration and action-angle-related functions. Orbit instances can
  now have arbitrary shapes. Full re-write of Orbit class (PR #384).

- Added support for 1D orbit integration in C (PR #354).

- Added a (JSON) list with the phase-space coordinates of known
  objects (mainly globular clusters and dwarf galaxies) for easy
  Orbit.from_name initialization. For ease of use,
  Orbit.from_name also supports tab completion for known objects in
  this list in IPython/Jupyter (PR #392).

- Added the galpy.potentials.mwpotentials module with various
  Milky-Way-like potentials. Currently included are MWPotential2014,
  McMillan17 for the potential from McMillan (2017), models 1 through
  4 from Dehnen & Binney (1998), and the three models from Irrgang et
  al. (2013). See PR #395.

- Added potential.to_amuse to create an AMUSE
  (http://www.amusecode.org) representation of any galpy potential,
  allowing galpy potentials to be used as external gravitational
  fields in AMUSE N-body simulations (#398).

- Added potential.toVerticalPotential to convert any 3D potential to a
  1D potential at a given (R,phi) [generalizes RZToverticalPotential
  to non-axi potentials; RZToverticalPotential retained for backwards
  compatibility].

- Re-wrote potential.MovingObjectPotential to allow general mass
  distributions for the moving object, implemented now as standard
  galpy potentials rather than with separate ForceSoftening class,
  which has now been removed (#355). Initialization keywords for
  potential.MovingObjectPotential have changed because of this in a
  non-backwards-compatible manner.

- Added support to combine Potential instances or lists thereof
  through the addition operator. E.g., pot= pot1+pot2+pot3 to create
  the combined potential of the three component potentials
  (pot1,pot2,pot3). Each of these components can be a combined
  potential itself. As before, combined potentials are simply lists of
  potentials, so this is simply an alternative (and perhaps more
  intuitive) way to create these lists (#369).

- Added support to adjust the amplitude of a Potential instance
  through multiplication of the instance by a number or through
  division by a numer. E.g., pot= 2.*pot1 returns a Potential instance
  that is the same as pot1, except that the amplitude is twice
  larger. Similarly, pot= pot1/2. decreases the amplitude by a factor
  of two. This is useful, for example, to quickly change the mass of a
  potential. Only works for Potential instances, not for lists of
  Potential instances (#369).

- Added support to plot arbitrary combinations of the basic Orbit
  attributes by giving them as an expresion (e.g.,
  orb.plot(d2='vR*R/r+vz*z/r')); requires the numexpr package.

- Switched default Sun's vertical height zo parameter for Orbit
  initialization to be the value of 20.8 pc from Bennett & Bovy
  (2019).

- Added IsothermalDiskPotential, the one-dimensional potential of an
  isothermal self-gravitating disk (sech^2 profile).

- Added NumericalPotentialDerivativesMixin, a Mixin class to add
  numerically-computed forces and second derivatives to any Potential
  class, allowing new potentials to be implmented quickly by only
  implementing the potential itself and obtaining all forces and
  second derivatives numerically.

- Added nemo_accname and nemo_accpars for the HernquistPotential,
  allowing it to be converted to NEMO.

- DehnenSmoothWrapperPotential can now decay rather than grow a
  potential by setting ``decay=True``.

- DehnenBarPotential and SpiralArmsPotential method now work for array
  inputs (PR #388, by @webbjj).
  
- Allow transformations of custom coordinate systems (positions
  and proper motions) to ICRS (ra,dec) and (pmra,pmdec).

- Allow orbit integrations to be KeyboardInterrupted on Windows as well 
  (#362 by Henry Leung)

- Add Python and C implementation of Dormand-Prince 8(5,3) integrator
  (#363 by Henry Leung)

- Added function galpy.util.bovy_conversion.get_physical to obtain the
  ro and vo parameters describing the conversion between physical and
  internal units as a dictionary. This works for any galpy object or
  lists of such objects.

- Improved efficiency of requesting an integrated orbit at the exact
  times at which it was integrated (~10x faster now).

v1.4 (2018-09-09)
=================

- Added ChandrasekharDynamicalFrictionForce, an implementation of
  dynamical friction based on the classical Chandrasekhar formula
  (with recent tweaks from the literature to better represent the
  results from N-body simulations).

- Added galpy.df.jeans with tools for Jeans modeling. Currently only
  contains the functions sigmar and sigmalos to calculate the velocity
  dispersion in the radial or line-of-sight direction using the
  spherical Jeans equation in a given potential, density profile, and
  anisotropy profile (anisotropy can be radially varying).

- Added CorotatingRotationWrapperPotential to galpy.potential: a
  wrapper to make a pattern wind up over time such that it is always
  corotating (for use in simulating corotating spiral structure like
  that of Grand, Kawata, Baba, et al.)

- Added GaussianAmplitudeWrapperPotential to galpy.potential: a
  wrapper to modulate the amplitude of any Potential instance with a
  Gaussian (growing from zero to the full amplitude and dying off
  again).

- Added a general class EllipsoidalPotential that is a superclass for
  implementing potentials with densities that are constant on
  ellipsoids (functions of m^2 = x^2 + y^2/b^2 + z^2/c^2). Also
  implemented in C. Implementing new types of ellipsoidal potentials
  now only requires three simple functions to be defined: the density
  as a function of m, its derivative with respect to m, and its
  integral with respect to m^2 (#348).

- Added PerfectEllipsoidPotential, the potential of a perfect
  ellipsoid (de Zeeuw 1985): this is a fully integrable
  (Staeckel-type), triaxial potential.

- Re-implemented TwoPowerTriaxialPotential and special cases
  TriaxialHernquistPotential, TriaxialJaffePotential, and
  TriaxialNFWPotential using the general EllipsoidalPotential class.

- Allow nested lists of Potential instances everywhere where lists of
  Potential instances were previously allowed; allow easy adding of
  components (e.g., a bar) to previously defined potentials (which may
  be lists themselves): new_pot= [pot,bar_pot].

- Add from_name class method of Orbit, which allows Orbit instances to
  be initialized using the coordinates of a named object found in SIMBAD.

- Add rguiding method of Orbit, to compute the guiding-center radius
  of an orbit. Also added Lz method to easily obtain the z-component
  of the angular momentum for different types of orbits.

- Defined Orbit initialization without any arguments (or, more
  generally, without specifying the vxvv initial phase-space input) to
  return an Orbit instances representing the Sun. Can therefore setup
  an Orbit representing the Sun's as o= Orbit().

- Allow Orbit instances to be initialized using a SkyCoord with
  position and velocity data, with optional Galactocentric frame 
  specification as part of the SkyCoord that is correctly propagated 
  to the Orbit instance. Requires astropy>3

- Added rtide and ttensor methods/functions for Potentials: tidal
  radius and tidal tensor.

- Added surfdens and evaluateSurfaceDensities method and function,
  respectively, for Potentials for evaluating the surface density up
  to a given z.

- Added potentials SphericalShellPotential and RingPotential for the
  potential of a spherical shell and a circular ring,
  respectively. Useful for talking about Newton's theorems.

- Switched default solarmotion parameter for Orbit initialization to
  be schoenrich (for the Schoenrich, Binney, & Dehnen 2010 solar
  motion wrt the LSR).

- Added Potential method r2deriv and function evaluater2derivs to
  evaluate the second derivative wrt the spherical radius. Also added
  convenience functions evaluatephi2derivs and evaluateRphiderivs.

- Added quasiisothermaldf method sampleV_interpolate that allows
  velocities at different positions to be sampled efficiently
  (quasiisothermaldf.sampleV only works for a single position). See PR
  #350.

- Add warnings/verbose configuration parameter to set level of
  verbosity of non-crucial warnings (like: "Using C implementation to
  integrate orbits").

- If astropy version > 3, Orbit.SkyCoord returns a SkyCoord object
  that includes the velocity information and the Galactocentric frame
  used by the Orbit instance.

- Tweaked coordinate-transformations to Galactocentric coordinates to
  be consistent with astropy's.

- Introduced general Force class of which Potential and
  DissipativeForce inherit, the former for forces that derive from a
  potential, the latter for those that do not.

- Introduced DissipativeForce, a superclass for all dissipative
  forces. ChandrasekharDynamicalFrictionForce is currently the only
  class that inherits from DissipativeForce.

- Re-arranged the package structure to better comply with the standard
  layout. All subpackages (e.g., galpy.potential) are now contained in
  subdirectories of the same name (e.g., galpy/potential/ rather than
  the old galpy/potential_src/).

- Made the code fully compilable on Windows with MSVC and test Windows
  builds automatically on appveyor (#333).

v1.3 (2018-02-06)
==================

- Added a fast and precise method for approximating an orbit's
  eccentricity, peri- and apocenter radii, and maximum height above
  the midplane using the Staeckel approximation (see Mackereth & Bovy
  2018); available as an actionAngle method EccZmaxRperiRap and for
  Orbit instances through the e, rperi, rap, and zmax methods.

- Added support for potential wrappers---classes that wrap existing
  potentials to modify their behavior (#307). See the documentation on
  potentials and the potential API for more information on these.

- Added DehnenSmoothWrapperPotential, a potential wrapper to smoothly
  grow a gravitational potential (e.g., a bar) following Dehnen
  (2000).

- Added SolidBodyRotationWrapperPotential, a potential wrapper to make
  a gravitational potential rotate around the z axis with a fixed,
  uniform pattern speed.

- Added DiskSCFPotential, a class that implements general
  density/potential pairs for disk potentials by combining Kuijken &
  Dubinski (1995)'s trick for turning a separable disk density
  [rho(R,z) = \Sigma(R) x h(z)] into a ellipsoidal-ish density, with
  the SCF basis-function-expansion approach of Hernquist & Ostriker
  (1992) for solving for the ellipsoidal-ish density's potential. This
  is a fully general Poisson solver (i.e., any density can be
  represented in this way).

- Added SoftenedNeedleBarPotential, a simple potential for a bar that
  consists of a needle softened by a Miyamoto-Nagai kernel (Long &
  Murali 1992).

- Added FerrersPotential, a class that implements the potential for
  triaxial ellipsoids (Binney & Tremaine 2008, Ch 2.5) with an option
  to give a pattern speed to the ellipsoid.

- Added SpiralArmsPotential, a class that implements the spiral arms
  potential from Cox and Gomez
  (2002). https://arxiv.org/abs/astro-ph/0207635v1 (#305)

- Added the Henon & Heiles (1964) potential

- Added an Orbit method to display an animation of an integrated orbit
  in jupyter notebooks (Orbit.animate).

- Added galpy.df.schwarzschilddf, the simple Schwarzschild
  distribution function for a razor-thin disk.

- Upgraded LogarithmicHaloPotential to allow it to be a triaxial
  potential.

- Upgraded DehnenBarPotential to a 3D potential following Monari et
  al. (2016) (#304).

- Generalized CosmphiDiskPotential to allow for a break radius within
  which the radial dependence of the potential changes from R^p to
  R^-p; also added C implementation of CosmphiDiskPotential.

- Changed default method for computing actions, frequencies, and
  angles for Orbit instances to be the Staeckel approximation with an
  automatically-estimated delta parameter.
  
- Added an option to the estimateDeltaStaeckel function to facilitate the
  return of an estimated delta parameter at every phase space point passed,
  rather than returning a median of the estimate at each point.

- Generalized actionAngleStaeckel to allow for different focal lengths
  delta for different phase-space points. Also allowed the order of
  the Gauss-Legendre integration to be specified (default: 10, which
  is good enough when using actionAngleStaeckel to compute approximate
  actions etc. for an axisymmetric potential).

- Allow transformations of (ra,dec) and (pmra,pmdec) to custom
  coordinate systems.

- Allow plotting of the spherical radius in Orbit.plot

- Allow plotting of arbitrary user-supplied functions of time in
  Orbit.plot, Orbit.plot3d, and Orbit.animate. 

- Added conversion to and from oblate spheroidal coordinates. Also
  added conversion of velocities to the momenta in oblate or prolate
  spheroidal coordinates (but not the other way around).

- Made SCFPotential compatible with GSL v2.

- Orbit methods now all return a scalar when called with a single
  time (see #247 and #294).

- Added a warning whenever the orbit-integration method that is used
  is different from the requested one (for when C integration falls
  back onto Python; see #286).

- Turn off changing the seaborn default plot configuration to that
  preferred by this code's maintainer; can be turned back on by
  specifying ``seaborn-bovy-defaults = True`` in the configuration
  file (see documentation). Old configuration files will be
  automatically updated to add this option (but remain otherwise the
  same).

- Added button to code examples in the documentation that copies the
  examples to the user's clipboard for easy pasting into a Python
  interpreter.

- Switched test suite from nose to pytest (#303).

- quasiisothermaldf.tilt return unit switched from deg to rad.

- streamdf.misalignment return unit switched from deg to rad.

- evolveddiskdf.vertexdev return unit switched from deg to rad.

- In quasiisothermaldf.py, the following prefactors were added
  to the following functions: [nsigma^2/2] --> pvT(), 
  [nsigma/2] --> pvRvT(), [nsigma/2] --> pvTvz(), 
  [vTmax/2] --> pvRvz(). This change was required to correctly 
  account for the Gauss-Legendre integration limits.

v1.2 (2016-09-06)
==================

- Added support for providing inputs to all initializations, methods,
  and functions as Quantities with units and for providing outputs as
  astropy Quantities. See pull request #258 and the documentation for
  full details.

- Added TwoPowerTriaxialPotential, a set of triaxial potentials with
  iso-density contours that are arbitrary, similar, coaxial ellipsoids
  whose 'radial' density is a (different) power-law at small and large
  radii: 1/m^alpha/(1+m)^beta-alpha (the triaxial generalization of
  TwoPowerSphericalPotential, with flattening in the density rather
  than in the potential, see Merritt & Fridman 1996, Binney & Tremaine
  2008). These include triaxial Hernquist and NFW potentials. Includes
  fast C implementations that allow efficient orbit integration in
  these potentials (<~5 ms / orbit).

- Added SCFPotential, a class that implements general
  density/potential pairs through the basis expansion approach to
  solving the Poisson equation of Hernquist & Ostriker (1992).  Also
  implemented functions to compute the coefficients for a given
  density function.

- Implemented galpy.actionAngle.actionAngleIsochroneApprox (Bovy 2014)
  for the general case of a time-independent potential, allowing
  action-angle coordinates to be computed for triaxial
  potentials. Previously, this module only supported axisymmetric
  potentials. Also allow the maximum number of terms in the expansion
  to be set object-wide and allow a fixed time-step to be used in the
  necessary orbit integration.

- Added an (experimental) interface to Binney & McMillan's TorusMapper
  code for computing positions and velocities for given actions and
  angles. See the installation instructions for how to properly
  install this.

- Re-defined the amplitude parameters of a few potentials to allow for
  easier setups with amplitudes provided as Quantities with
  units. This is the case for FlattenedPowerPotential,
  PowerSphericalPotential, and PowerSphericalPotentialwCutoff,
  CosmphiDiskPotential, LopsidedDiskPotential, and
  EllipticalDiskPotential.

- Added a module for modeling the effect of a subhalo impact on a
  tidal stream (galpy.df.streamgapdf); see Sanders, Bovy, & Erkal
  (2016). Also includes the fast methods for computing the density
  along the stream and the stream track for a perturbed stream from
  Bovy, Erkal, & Sanders (2016).

- Added functions to galpy.df.streamdf to compute the length of the
  stream, the density along the stream quickly (in various
  coordinates, including custom sky coordinates), to compute the
  probability p(freq_parallel,angle_parallel), and to estimate the
  number of encounters with DM subhalos. Also allow the stream track
  to be computing using the new actionAngleTorus (this last addition
  is still very experimental).

- Added PseudoIsothermalPotential, a standard pseudo-isothermal-sphere
  potential.

- Added KuzminDiskPotential, a potential represented by a razor thin
  disk

- Allow transformations to custom sets of sky coordinates in
  galpy.util.bovy_coords.

- Added the spherical radius as an Orbit method.

- Added the spherical-radial force as a Potential method (rforce) and
  function (evaluaterforces).

- Support for flipping the velocities of an orbit in-place (useful for
  backwards integration).

- quasiisothermaldf input ro replaced by refr to avoid clash with ro
  that specifies units (see above).

- Properly intercept CTRL-C (SIGINT) signals during orbit integration
  in C, allowing long orbit integrations to be interrupted without
  killing an entire Python session.

- Internally use astropy.coordinates transformations to transform
  between (ra,dec) and (l,b). Can be tuned using the astropy-coords
  configuration parameter. Also allow general epochs for the (ra,dec)
  specification.

v1.1 (2015-06-30)
==================

- Added Python 3 support: in particular, Python 3.3 and 3.4 are now
  supported; earlier 3.* may also work, but haven't been
  tested. Python 2 and 3 are supported using a single common codebase.

- Added SnapshotRZPotential and InterpSnapshotRZPotential potential
  classes: these can be used to get a frozen snapshot of the potential
  of an N-body simulation into galpy. SnapshotRZPotential directly
  calculates the potential and forces using direct summation;
  InterpSnapshotRZPotential builds an interpolation table (it's a
  subclass of interpRZPotential and can be used in the same way). This
  code was mainly written by Rok Roskar.

- Added KuzminKutuzovStaeckelPotential, a Staeckel potential that can
  be used to approximate the potential of a disk galaxy (see Batsleer
  & Dejonghe 1994).

- Added MN3ExponentialDiskPotential that gives the approximation to a
  radially-exponential disk potential as three Miyamoto-Nagai disks
  from Smith et al. (2015; arXiv:1502.00627v1)

- Added PlummerPotential, a standard Plummer potential.

- Add support for converting potential parameters to NEMO format and
  units: nemo_accname and nemo_accpars (both instance and general
  Potential method).

- Added nemo/ directory for C++ implementations of additional NEMO
  potentials (not included in the NEMO release); add PowSphwCut.cc for
  PowerSphericalPotential2Cutoff and Makefile to compile and install
  it. This allows gyrfalcON simulations with MWPotential2014.

- Allow user to directly specify the integration step size to use in
  orbit integration.

- Better implementations of vcirc, eipfreq, and verticalfreq for lists
  of potentials that allows for negative amplitude components.

- Improvements to streamdf: add progIsTrack keyword to specify that
  the progenitor= keyword actually specifies the desired starting
  phase-space point of the track; the phase-space point of the
  progenitor is calculated. Refactored streamdf setup to make this
  easy to implement.

- Orbit fitting can now be performed in custom sky coordinates
  (requires one to specify customsky=True and to implement and pass
  the functions (a) lb_to_customsky= and (b) pmllpmbb_to_customsky=,
  similar to lb_to_radec and pmllpmbb_to_pmradec). For example, this
  allows one to do an orbit fit in the GD-1 frame of Koposov et
  al. (2010).

- Orbit.time now returns the times at which an Orbit is integrated if
  called without arguments.

- Slightly improved implementation of actionAngleStaeckel.py (more
  robust umin/umax finding).

v1.0 (2014-12-10)
==================

- Added MWPotential2014: a Milky-Way-like potential fit to a bunch of
  relevant data on the Milky Way; supersedes MWPotential, which is
  still included; changed many examples to use this new potential;

- Changed default integrator to symplec4_c;

- Changed default vo and ro to 220 km/s and 8 kpc, respectively;

- Allow Orbit initialization to specify a distance and velocity scale
  that is then used to output distances, velocities, energies,
  actions, etc. in physical coordinates;

- Added an orbit-fitting routine (Orbit.fit).

- Added virial radius of NFW potential, allow initialization of NFW
  potential with concentration and mass;

- Added potential.mass to return the mass enclosed for individual
  potential instances; both spherical and axisymmetric potentials are
  covered.

- Sped up many of the functions in galpy.util.bovy_coords by removing
  scipy.frompyfunc dependency;

- Added galpy.util.bovy_conversion.dens_in_gevcc,
  galpy.util.bovy_conversion.force_in_10m13kms2,
  galpy.util.bovy_conversion.dens_in_criticaldens,
  galpy.util.bovy_conversion.dens_in_meanmatterdens.

- Much improved test coverage.

- Added planarPotential.LinShuReductionFactor to calculate the
  reduction factor for the response of a kinematically warm population
  to a spiral perturbation.

- Added non-axisymmetric DFs to the top-level and the documentation.

- New streamdf track calculation (see arXiv_v2/published version of
  Bovy 2014); better handdling of coordinate-transformation
  parameters in streamdf.

- Installation now prints informative message about whether or not the
  C extensions were installed.

- More informative warning messages when C functions are not used.

- Fix issues with non-square grids in the C implementation of
  interpRZPotential.

- Added Orbit.flip to generate new Orbit instances with flipped
  velocities.

- Improved actionAngle frequencies for circular orbits.

- Removed actionAngleFlat and actionAnglePower, because they are
  superseded.

- Added hasC_dxdv member to Potential instances to indicate whether or
  not they can be used with integrate_dxdv

- Add C implementation of PowerSphericalPotentialwCutoff;

- Moved MovingObjectPotential, BurkertPotential, and interpRZPotential
  to top level; better implementation of interpRZPotential;

- Better handling of vo,ro, and solarmotion in Orbit instances (Orbit
  initialization value is now used to generate RA, Dec, etc. outputs);

- Added --no-openmp installation option to allow installation without
  OpenMP support (workaround for clang not supporting OpenMP; not
  necessary anymore);


v0.1 (2014-01-09)
==================

- Initial release