Matching

- Minor docs fixes.

- Players are now copied via `copy.deepcopy` when a game is created and the
copies are used, leaving any originals unchanged.
- Formalise test and Python requirements in `setup.py`.
- Revert flaky forgetting fix from v1.2.1 and correct the flaky tests that were
causing the issue.
- Replace the `Game` class with `BaseGame` and make it a metaclass via
`abc.ABCMeta`.
- Fix bugs in documentation stopping build.

- Update the self-citation information in `paper.bib` to `v1.3`.

- Finish documentation.
- Complete paper for submission to JOSS.
- Catch flaky forgetting bug in `Player`.

- Implement the stable roommates problem.
- Add example tests to all games.
- Flesh out documentation.

- Implemented the student-allocation problem.
- Added capability for large game creation from dictionaries.