Use of Doxygen

[RaphaelPetrequin]

@Splinter3D/maintainers

While implementing a new ui widgets properly, I tried to use doxygen and I wasn't aware of how powerfull the docs' generation was !
I did push my work here: #21 on the ui/ and app/ part.

Impementing a standard like putting precise doxygen comments on .hpp would help for future collaboration and maintainance.

Can we use doxygen on our project to automatically create precise documentation about the code structure ?

It would force us to comment properly our code, and let us focus on creating more technical documentations / user docs / tests docs.