Backport the Doxygen changes to the 2.2.x branch. No functional changes,

however backporting these doxygen fixes makes it significantly easier to diff
trunk and the 2.2.x branch, to sort out what's what. And we might as well
release with nicer doxygen markup.

Submitted by: Neale Ranns <neale ranns.org>
Reviewed by:  Ian Holsman


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@292540 13f79535-47bb-0310-9956-ffa450edef68