Timezones

[thekid]

Implements feature request #4

$calendar= (new ICalendar())->read($input);

$start= $calendar->date($calendar->events()->first()->dtstart()));  // a util.Date instance

[thekid]

Now that text.ical.Date instances are used often in conjunction with util.Dates, it's probably wise to rename the first to IDate to avoid import conflicts. Can this be done in a BC-break-free manner?