Airball

- Save and load `StellarEnvironment` (uses Python's `pickle` underneath)
- Fixed issue where randomly generated stars were generated uniformly, but not isotropically.
- Bug fixes.

- Updated example data folder structure.
- Clarified differences between uniform and log-uniform in IMF
- Extended functionality, speed-ups when processing multiple stars at once.
- Added rotate_into_plane, hyperbolic_plane, maxwell_boltzmann_dispersion_from_scale. Updated unit_vector and angle_between to handle lists of vectors.
- Moved _rotate_into_plane to tools. Refined hash handling.
- Clarified the way astropy.units is imported.
- Added option to return empty Stars object. Added ability to concatenate Stars objects with +.
- Simplified Distribution class and subclasses.
- Refined encounter_rate call.

- Overhauled API documentation.
- Clarified and consolidated some functionalities.
- Added ability for `Stars` to be generated directly from a `StellarEnvironment` with `Stars(StellerEnv(), size=10)`.

- Improved hybrid switching.
- Successive and Concurrent flyby functions
- Deeper Stars functionality
- More consistent Stellar Environments
- More Unit Tests

Hybrid Integrator
Added hybrid integrator switching between `WHFast` and `IAS15` to more accurately resolve 3-body interactions.
Fixed major issues with successive flybys.

**Full Changelog**: https://github.com/zyrxvo/airball/compare/v0.1.0...v0.2.0

The first reasonably useful version.

Simply `pip install airball` to get started.
It is still likely to have a massive overhaul, refactoring, and API changes.
`import airball` operates in an expected way with a relatively shallow structure.