Draft: docs: Generate documentation with sphinx

[Melkor333]

This PR will add documentation generation with sphinx.
It's using (a manually patched version of) md-click (I sent upstream a mail hoping they might merge one of the fixes...) and autodocs to generate docs for the most relevant code.

TODOs:

• Make the index.rst a bit more pretty. Optimally it would show the content of the README.md. Maybe we should convert it to rst and then just merge it into the index.rst 🤔
• We really need to write some docs on the config.toml
  • The examples in the test folder are very useful and might be reused for this.
  • As seen in Support all aptly commands' parameters/options #120 it's not always clear what Features even exist -> we need reference docs as well. I was thinking about defining a json-schema and using jsonschema-markdown. This way we also get validation "for free", something that should happen at some point.

[Melkor333]

This should also close #113 when finished.

[Melkor333]

Got internal feedback that maybe gitbook or vuebook might be a "more modern" approach than going back to sphinx... Since everything is markdown the only missing piece would be the pydocs which could probably be converted to md with something like pydoc-markdown