Improve TRIGGER DURATION parsing logic

[jessejoe]

TRIGGER DURATIONs can also take the form TRIGGER;VALUE=DURATION:-PT30M. The existing logic only accounts for TRIGGER:-PT30M.

This can be tested with any of the NHL ical schedules from this season, e.g. https://www.stanza.co/api/schedules/nhl-sabres/nhl-sabres.ics .

Before:

In [2]: cal = ics.Calendar(requests.get('https://www.stanza.co/api/schedules/nhl-sabres/nhl-sabres.ics').text)

ParserError: Could not match input to any of ['YYYY-MM-DDTHH:mm']

After:

In [2]: cal = ics.Calendar(requests.get('https://www.stanza.co/api/schedules/nhl-sabres/nhl-sabres.ics').text)

In [3]: cal.events[0].alarms[0].trigger
Out[3]: datetime.timedelta(0, 1800)

[C4ptainCrunch]

Great, thanks !