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
DIARY-FILE.
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
non-marking.
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)