Documentation enhancement

[roblabla]

The documentation PR was a good first step in the right direction, but it still needs a lot of work:

• The main page is currently set to the README. This doesn't make a whole lot of sense, it should instead be a high level presentation of libtransistor, with a list of "modules"
• Talking of modules, we should use doxygen's grouping system such that we generate a better looking docs. https://www.stack.nl/~dimitri/doxygen/manual/grouping.html
• Right now the list of functions is hidden deep. It'd be nice to find a way to put this in the forefront.

[misson20000]

Kinda silly to add this to the list, but the default Doxygen theme looks terrible. If someone wants to write up some better CSS to better match our other web design (see SwIPC), I'd appreciate it.

[misson20000]

If anyone wants to play with CSS, here's a WIP stylesheet to make Doxygen look a little more like SwIPC: https://gist.github.com/misson20000/d9d1ec6d8afaa4cfd1a670221429d543

Looks like this right now. (screenshot not marked down as an image because it's really tall)

Still needs quite a bit of work, but the default Doxygen theme is just so bad.

[qsypoq]

I started to work on the CSS, suggestions are welcome:
https://qsypoq.github.io/libtransistor/