* Further clarify hook callback return convention

* Further clarify hook callback return convention
* Place some trace calls into context
* Every hook callback implementation now has the same comment format
* Document hitherto undocumented hook callbacks
* Always trace the handler, whether it gets to write its content or not
* Clean up stale 1.3 comments in handler callback
* Document quick_handler callback according to a conversation Googled up from
  new-httpd in 2002
* Change callback names so all follow the same format: the hook name with a
  prefix
* Add a callback handler for the enigmatic ap_hook_monitor

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@479471 13f79535-47bb-0310-9956-ffa450edef68