Backport rewrite guide improvements from trunk

Backport rewrite guide improvements from trunk

Sync reorganized and expanded mod_rewrite documentation from trunk:
- Rewritten index with structured navigation
- Expanded flags reference with new examples (chain, cookie, DPI)
- Renamed htaccess doc to 'Per-directory Rewrites' with new sections
  on path stripping, RewriteBase, and loop behavior
- Expanded tech.xml with detailed per-directory processing explanation
- New recipes in remapping.xml: HTTPS behind load balancer, ACME
  exemption, trailing-slash handling, front-controller patterns
- Added prg: map Python example in rewritemap.xml
- Cross-reference links and glossary terms throughout
- Fixed incorrect <since> tags: SameSite is 2.4.47, UnsafePrefixStat
  is 2.4.60, UNC is 2.4.63 (were erroneously marked 2.5.1)
- Removed N flag iteration-limit paragraph (trunk-only feature)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1934664 13f79535-47bb-0310-9956-ffa450edef68