Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 start_events

 end_events

 set_event(Arg1)

 set_event(Arg1, Arg2)

 add_event(Arg1)

 reply_ical(Arg1, Arg2)

 ical(Arg1, Arg2)

 ical_stream(Arg1, Arg2, Arg3)