Extract iCalendar events from current buffer.
This function searches the current buffer for the first iCalendar
object, reads it and adds all VEVENT elements to the diary
It will ask for each appointment whether to add it to the diary
unless DO-NOT-ASK is non-nil. When called interactively,
DO-NOT-ASK is nil, so that you are asked for each event.
NON-MARKING determines whether diary events are created as
Return code t means that importing worked well, return code nil
means that an error has occurred. Error messages will be in the
buffer `*icalendar-errors*'. (fn &optional DIARY-FILE DO-NOT-ASK NON-MARKING)