Makes each flag a top-level section in this doc, thereby giving it a

navigation link in the right navigation box. I think that makes this
page much more useful, particularly when it becomes the primary resource
for rewriterule flags and their use.
Also adds some detail on several of the flags.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@894539 13f79535-47bb-0310-9956-ffa450edef68