[PATCH] doc: improvements to doxygen and protocol docs

[Bill Spitzak]

This set supersedes my outstanding patches and consists of several
patches that should be independent if you wish to pick & choose:

1,2,3 : some minor fixes to doxygen output
4: rearrangment to put wl_event_queue methods into their own section
5: intro text for the libs, this is most questionable as I wrote it
6,7,8 : Add object types and links and clean up protocol docs