This is not 100% fietsboek, but it's closely related, and I don't think
setting up a separate site for hittekaart is worth it. At the moment,
this is a bit WIP, as the module sits in its own branch in the
hittekaart repository, but in the long run I want to use this. It also
is an experiment to see how well PyO3 works, as we potentially want to
migrate other parts of fietsboek to Rust in the future (no specifics
yet, but keeping the option available is nice).

In tox.ini, we disable -f for sphinx-apidoc, so that it doesn't
overwrite the modules.rst file. This means that the directory must be
clean if you re-generate the docs (it is on the CI server).

Also, we un-gitignore the modules.rst and hittekaart_py.rst files, as
special cases. The others are still auto-generated, so all good, but
these two we need.

This includes a bump to Python 3.11, as we use datetime.UTC which was
only added in 3.11. We could go back and change those instances to
datetime.timezone.utc, but why artificially stick to Py 3.10.