Fest

* Added Slack integration

Updated `sync_events()` method to handle canceled events.

`source_events` is now a dictionary of the form:

python
{
'upcoming': [event, event, _],
'canceled': [event, event, _]
}

* Add `event_state_filter` option to facebook event request
* Add `delete_event` option to Google

* Handle recurring facebook events

* Alpha release