Inline documentation format

[Mohamed Ikbel Boulabiar]

The most used one is doxygen.
And I verified it can generate any other type of common documents
format (Latex, html, pdf, etc..)

Some tools exist to generate docbook documents, so with the current
process of putting all X documentation in one place with that format,
we can have similar thing with Wayland.

Nikolai, if you have some time, send some patches for doxygen and I
think Kristian will apply them.

Thanks,

i