Autogenerate Docs & more Documentation

[domenukk]

Right now all doc is inside the code.
We should set up a sphinx instance or some other nice way to make the API browseable.
To get started with sphinx, there is this project (not super actively maintained) which may just be enough or this blog post that seems to be a bit more work, going through doxygen first.
I didn't find a way to get the sphinx thing going directly, without additional tools, but maybe there's an easy way.

Once we decided on a documentation format, we can start writing more docu.

[vanhauser-thc]

What I like about doxygen is how it looks when you document, and that you can auto-generate images about dependencies.
There are a few things that I do not like (eg. the brief text is too short in the overview IMHO) but these might be customizable.

but @hexcoder- also wanted to have a look at solutions because he had good ideas like maybe there is a solution out there that warns if the description does not match the declaration, or that can pre-generate the comment stub from a declaration, etc.