visibility, phpdocs, minor cleanup
reformatting
some renaming
No double entities escaping. Fixes #4
Cache expiring depends also on changelog of discussions

If discussion plugin feed is requested, it checks for cache expiring the
comment changelog for changes as well.
Update plugin.info.txt
Merge pull request #5 from Klap-in/branch

Cleanup, no double escaping in feed and proper cache handling for discussions.