Vacation calendar based on event type instead of keyword

[danielmarbach]

I was looking into the vacation calendar. Pretty neat! I was wondering why the vacation calendar uses keywords instead of event types? Calendar already has an "out of office" type that could be used automatically.

[erickoledadevrel]

Unfortunately there isn't a stable way to determine if an event is of the special out-of-office type in the Calendar API. Once that becomes available I'd add support for it in addition to keywords, but I think it would be good if the script also used keywords, since I don't think everyone uses those new types of events.

[simaoafonso-pwt]

See #209