Ashpy

- Restorer no longer throws an exception when it cannot find a `checkpoint_map.json`
- Trainers generate a `checkpoint_map.json` for each model selection folder
- Refactor out `os.path` et similia in favor of `pathlib`
- Add tests for correct callbacks restoration
- Fix some pylint errors in the tests

- New Project structure -> `src/ashpy` & new way to handle requirements
- Automate test suite with `tox`
- New tests!
- Add `ashpy.restorers` module facilitating restoration from `tf.train.Checkpoint`
- Bugfixes

Metrics:
- SWD: Sliced Wasserstein Distance
- MSSIM: MultiScale Similarity

Distribution:
- Fixed Bugs related to distribution strategy

Losses:
- Add Hinge Loss

Code Style:
- Standardize the usage of the reduction inside losses

Version:
Fixed version number