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.

https://docutils.sourceforge.io/RELEASE-NOTES.html#release-0-21-2024-04-09.

I think there are legitimate use cases and flat out not allowing any
lambda to be assigned to a variable is very restrictive.

It's a start, now it's there and can be improved!

We have so many nice docstrings, but they aren't really rendered
anywhere (expect locally in your IDE), as we did not include the API
docs anywhere.

This change uses sphinx-apidoc to generate autodoc stubs for Sphinx, so
that the docstrings are actually rendered to HTML. This is not perfect
yet (I'm not too happy about the default modules.rst simply listing one
package), but it is good enough for the start and makes it possible to
actually browse the docstrings in a browser.