At long last, promote mod_cache and friends out of experimental/.

Also, take quick pass through docs files to remove experimental label for them.

Reviewed by: Paul Querna, Bill Stoddard, Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@106737 13f79535-47bb-0310-9956-ffa450edef68