github: support defining handlers for events.
github: support defining handlers for events.

Add two handlers, push and watch


Former-commit-id: 22cb54515f13c0566ed2431e302f4cb659a61860 [formerly 0641d5bd7ff4c751cbb39c21c8dc3cbe398384eb]
Former-commit-id: 59560b476b62ed28f3d45b7328e634ab16696553
torhve/ivar2,haste/ivar2,torhve/ivar2,torhve/ivar2