[Xcb] documentation patches

[Michael Stapelberg]

Hi Uli,

Excerpts from Uli Schlachter's message of 2012-03-26 14:54:10 +0200:
> No idea how much of this should be fixed before the patches are merged. These
> docs are definitely better than no docs. But something should happen, so if you
> want to ignore my comments from above, say so and the patch can get merged
> instead. But most of these TODOs should be resolved before this ends up in a
> released xcb-proto.
Thanks for your comments. As you suggest, I would love to see my patches merged
first, and then we can iterate based on that.

Best regards,
Michael