Test and build docs on GitHub Actions

[hugovk]

For #18.
Fixes #22.

This PR adds workflows to run the tests and build the docs with GitHub Actions.

Tests

It's only testing the upstream supported versions of Python: 3.8-3.11: https://devguide.python.org/versions/

I didn't add uploading of coverage to Coveralls. I usually use Codecov myself, so have left Coveralls out for later addition.

Docs

The docs are built and uploaded as an "artifact" to GitHub Actions. This means you can download a zip of the built docs from the build summary tab.

(I usually use Read the Docs, and enable the PR build previews, so you get a hosted page for each PR.)

Deploy

This PR does CI, not CD. I didn't attempt to add deploying to PyPI or upload of docs, but I recommend doing this later. PyPI's "Trusted Publishers" is an excellent choice along with the 'pypi-publish' GitHub Action:

• https://blog.pypi.org/posts/2023-04-20-introducing-trusted-publishers/

I also didn't delete the old .travis.yml yet in case you need it for the deploy reference.

Demo

• Test: https://github.com/hugovk/calmap/actions/runs/5723408597
• Docs: https://github.com/hugovk/calmap/actions/runs/5723408599

[hugovk]

Updated to add 3.12, but this fails due to #22:

https://github.com/hugovk/calmap/actions/runs/7369885527/job/20055674868

So also updated to replace distutils.version with packaging.version, which passes:

https://github.com/hugovk/calmap/actions/runs/7369888801