This changes the behaviour of mergeYupYdown: afterwards, the parallel
slices are not valid

* next: (93 commits)
  Fix use of abs in fieldgenerators
  Fix use of abs in utils.hxx
  Fix use of abs in cyclic_reduction
  Fix use of abs in imex-bdf2 solver
  Fix abs use in slepc solver
  Fix use of abs in rkgeneric
  Improve some comments; use uniform initialisation more consistently
  Use `Options::force` to overwrite options quietly
  Default initialise field sizes and Field::bndry* status
  Default initialise boundaryIs{Copy,Set} in FieldData
  Default initialise some Field3D/2D members
  Add move constructor for Field2D
  Add swap function for Field2D
  Add move constructor for Field3D
  Make test-command-args quieter
  Add test for clobbering datadir from commandline
  Fix:Escaping in makefile
  Documentation improvements
  Improve documentation
  Make sure command line short-options override options file settings
  ...

* next: (347 commits)
  Parameterise FFT tests over both even- and odd-length real signals
  Fix bug in `irfft(Array)`: length of original signal is needed
  Add Array::resize to simplify changing the size of an Array
  Use type alias instead of typedef
  Move ShiftedMetric::cmplx/cmplxLoc into shiftZ; make shiftZ const
  Fix shiftedmetric test fixture
  Move some initial setup into ShiftedMetric test fixture
  Add more ShiftedMetric tests
  Add region argument for test field-field comparisons
  Basic test for shiftedmetric
  Add test helpers for filling Fields with values
  Move map and function definitions into source file for bout_types
  Support loc argument to Laplacian::tridagCoefs
  Fix elm-pb MMS test boundary conditions
  Remove deprecated invert_laplace functions from tests
  Deleting unused example code
  Almost all invert_laplace calls removed
  Removing more invert_laplace uses
  Make absence of fftw-wisdom non-fatal in configure
  Use unique_ptr for LaplaceXZcyclic::cr
  ...

Forward-FFT whole field, then inverse-FFT for each parallel
slice. Will make it easier to generalise to multiple parallel slices

Tighten up the unit tests to catch this

…gister

…hods

- Remove unused variables
- Store mesh and check it's the same as the field to be
  interpolated/integrated
- Store interpolations as unique_ptrs to avoid potential memory leaks

* next: (99 commits)
  Fix typo in documentation
  Silence warnings in MMS/time
  Remove some commented out bits from MMS/time
  Test fix: don't use adaptive time stepping when measure time scaling
  Further generalise derivatives unit test to fourth order methods
  Fix comments in derivatives test
  Be more generous with allowed order to count as pass
  Add line to trace manipulation section
  Update unit tests for assignment from non-finite
  Fix typo
  Allow assignment with non-finite but allocated data
  Fix links in intro
  Add section on analyzing/manipulating trace files
  Add Extrae+Archer info
  Update intro to include Extrae/Paraver
  Remove setLocation() in Field3D::operator=(FieldPerp)
  Add helper function for filling fields with function at each point
  Test all first and second derivatives in X, Y and Z
  Actually remove the checkData calls
  Update unit tests for checkData removals
  ...

Should be done better by actually calculating the arc length of the
field line

* next: (57 commits)
  Make messages(de) more consistent
  Fix expr.hxx
  Improve translation
  Update name pf helper function
  Add German translation
  Update generated file
  Extend README
  String changes for translation
  Auto: update libbout.pot
  Replace IsField*Equal* predicates with templated versions
  Use nullptr as default Mesh* argument for Laplacian::create
  Fix bug in DST option for cyclic solve
  Add initial simple tests for advection derivatives
  Increase grid size used in test_derivs unit tests
  Add 'using namespace bout::globals;' for new unit test files.
  Ignore hidden and temporary files
  Pass mesh_in in initializer list of FCIMap::FCIMap constructor
  Pass parameter pack by forwarding-ref, function by const-ref
  Use bout::globals::dump in BOUTMAIN macro
  Use bout::globals::dump in SlepcSolver
  ...