Added
-----

- Optional dynamic interplanetary frame via the `env.jpl.dynamic_frames`
  configuration variable
- Single function to retrieve local orbital reference frame rotation
  matrix
- Creation of the `StateVector`  class as parent of the `Orbit` class.
  It has
  the same behavior as `Orbit` but can't be extrapolated.
- Covariance matrix can now be expressed in a reference frame
  independent of its orbit.

Modified
--------

- The list of `bsp` and `tpc` files to read for the `beyond.env.jpl`
  module to work
  should be provided to the `env.jpl.files` configuration variable,
instead of the previous
  `env.jpl`.
- The `beyond.utils.matrix.expand()` function now takes a single
  argument.
- Refactoring of `beyond.propagator.keplernum` and `beyond.orbits.man`
  to remove unused method argument
- Refactoring of `beyond.frames.frames` to avoid using metaclasses. This
  has huge code repercussions
  and affected a large number of files.
- The `skip_if_no_mpl` test decorator is replaced by `mpl`

Fixed
-----

- Wrong assumption on the config dict structure now leads to a
  ``ConfigError``
- The BSTAR drag term of the TLE format can be above 1e-1