mod_proxy: add a link to the status flag table

mod_proxy_hcheck: add some hyperlinks, improve syntax highlight, add some missing trailing dot, be more consistent with other modules in the way 'Syntax' lines are displayed

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1832294 13f79535-47bb-0310-9956-ffa450edef68