Add model TinyIntegerField/PositiveTinyIntegerField

[le717]

This starts adding support for the TINYINT field, with an unsigned version available too.

Building proper model fields (i.e., not simply subclassing IntegerField and overriding db_type) is still very foreign to me, so I appreciate any and all suggestions to help me learn how to better make these. 😃

TODO

• [ ] Confirm actual construction is correct
• [x] Add test model/migration
• [ ] Add/run tests
• [ ] Add documentation
• [ ] Any feedback you have

Documentation

• https://mariadb.com/kb/en/tinyint/
• https://dev.mysql.com/doc/refman/en/integer-types.html

[adamchainz]

I guess it would be good to add this for completeness, but I'd like to understand a bit more about why you'd like such a field type. It's best to add issues before working on features, to provide context. Everything added to the package will need maintaining until the heat death of the universe.

Also workflow-wise, it'd be best if you could set up pre-commit locally, so the CI service doesn't need to push fix commits.