Added per feed author muting

Added a new function, authormute, which gives the ability to mute
individuals authors in one feed. This is useful in feeds from big
sites, TheVerge for example, where you only want to read content from
certain authors.

Additionally, rather than triggering the fever-filter script on a cron,
it is possible to hook the main Fever refresh script. The location is:
fever/firewall/app/libs/fever.php, line 3311 at the end of the function
called Infiniterator. If you call the fever-filter script there, it
gets called only once after Fever has finished.