Convert iCalendar (.ics) data files to pcal data files

The iCalendar format (.ics file extension) is a standard (RFC 2445)
for calendar data exchange. Programs that support the iCalendar
format are: Google Calendar, Apple iCal, Evolution, Orange, etc.

The iCalendar format have many objects like events, to-do lists,
alarms, journal entries etc. ical2pcal only use the events in the
file showing in the pcal file the summary and the time of the event,
the rest information of the event like description or location are
commented in the pcal file (because usually this information does
not fit in the day box).

Currently automatic detection and conversion to local time of time
values in UTC is implemented. All other time values are assumed as
local times.