Add the feed id to the Pubsubhubbub callback url
Use the feed's self link for the Pubsubhubbub topic url
Add topic update to Pubsubhubbub migration
Add automatic Pubsubhubbub resubscription on expiration
Small bugfix in pshb route
Add Pubsubhubbub unsubscribe support
Fix expiration check of feeds without a pshb expiration
Make sure the pshb topic URL is a valid URL, and use the feed url if it isn't