Improve API doc visuals

[bk138]

• using sphinx and breathe:
  • https://devblogs.microsoft.com/cppblog/clear-functional-c-documentation-with-sphinx-breathe-doxygen-cmake/
• standalone doxygen
  • https://mcss.mosra.cz/documentation/doxygen/
  • https://stackoverflow.com/questions/36064976/using-doxygen-in-read-the-docs

[Quadrisheriff]

Hi I can work on this , doxygen will be very perfect

[bk138]

@Quadrisheriff Very welcome!

We already use doxygen, but it's customisation possibilities are quite limited. I reckon that the approach using sphinx and breathe will yield the best visual results.