CI

[dgelessus]

I need to set up some kind of CI service (GitHub Actions, Travis, ...) to automatically run tests (once there are any, see #7) and mypy. This might also be a good opportunity to set up additional checker tools (such as flake8).

The tests should be run on multiple Python versions and OSes. The checker tools only need to run on one configuration (they only perform static analysis that is not dependent on the Python version and OS used to run the tool). tox could be used to manage test/tool execution on different Python versions.

[dgelessus]

Added a Tox configuration in 1a416de and a GitHub Actions CI workflow in 3a805c3.

[dgelessus]

Also added flake8 in f690caa.