Added 'update' as a possible action.
Added 'update' as a possible action.

- Total list is now create, update, save.
- Aligned them with the rails active_record callbacks :after_create, :after_update, :after_save

Fixes #31

BrilliantChemistry/NotifyOn,digerata/NotifyOn,BrilliantChemistry/NotifyOn,digerata/notify,BrilliantChemistry/NotifyOn,digerata/NotifyOn,digerata/notify,BrilliantChemistry/NotifyOn,digerata/NotifyOn,digerata/notify