improved db performance of fof_update_feed, removed some dead code for the get_item_tags functions (still available, just commented out).  Still need to perform further testing to ensure everything works as expected
squashed a few bugs in the new fof_update_feed function (and assosciated fof_db_add_items functions)
resolved issue 187, saved some memory when fetching subscription tags.  Fixed some more error in new fof_update_feed
resolved issue 186 - subscription table now gets cleaned up properly when a feed is deleted
fixed empty array issue when applying subscription tags
fixed issue 190, newly added items not being marked as unread
removed a lot of dead code, see issue 190
merged development branch into master
eliminated more dead code.  Removed useless wrapper functions in fof-main.php, replaced them with their equivalents in fof-db.php

removed useless wrapper functions

fof_is_subscribed -> fof_db_is_subscribed
fof_mark_unread -> null.  Was never used anyway
fof_mark_read -> null.  Was never used
fof_get_unread_count -> fof_db_get_unread_count