rewrite introductory section which lists the various modules

required for proxy

show more protocol modules (and in tabular form)
separate protocol modules from balancing

(mod_proxy_fdpass still omitted for now)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1032399 13f79535-47bb-0310-9956-ffa450edef68