add 'created' event property

birthdays-cal.py

@@ -86,6 +86,7 @@ def make_event(person, year):
         event_date.year, event_date.month, event_date.day))
     event.add('dtstart',     event_date)
     event.add('duration',    one_day)
+    event.add('created',     datetime.datetime.utcnow())
     event.add('last-modified', datetime.datetime.utcnow())
     return event