Fix a link as spotted by Benoit Wery in the comment system. (backport of r1818059)

Synch with trunk doc:
   - Add some quotes to improve syntax hightlight
   - Remove some trailing spaces.
   - Mention mod_macro (backport of r1436578)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1818061 13f79535-47bb-0310-9956-ffa450edef68