Change doxygen section names to generate nicer links

Rename Doxygen documentation sections to generate nicer links

Doxygen follows some (undocumented) rules when generating HTML
links. Unfortunately for us, the form `@defgroup FOOBAR` will actually
generate a page called `F_O_O_B_A_R`, which is really really ugly. It seems
doxygen replaces a single `_` with two underscores, and an upper-case
leter itself is surrounded by underscores as well.

Luckily we can avoid all this if we use hyphen-delimited, all lowercase
names for our doxygen sections; in which case the actual link pages
resemble the names the most.

Unfortunately because we have documentation EVERYWHERE and this naming
convention is also everywhere, this commit touches a lot of files,
albeit in a trivial manner.

Change-Id: I9f9af585ebe51e4337ee764bf45e68c871021f61
Reviewed-on: http://review.couchbase.org/43199
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>