Create a a documentation browsable online living inside the codebase

[yacineMahdid]

Even though we won't have much, having the boiler plate of the documentation will allow us to easily extend it as we go. As time goes on this task will become less and less appealing.

[yacineMahdid]

It seems that Doxygen is good choice for this type of project however after some digging the trio of Doxygen + Breathe + Sphinx is more useful. Plus we can host that documentation on readthedocs for free which is very good!

Here is a link to get started that I will follow: https://devblogs.microsoft.com/cppblog/clear-functional-c-documentation-with-sphinx-breathe-doxygen-cmake/