Undocumented predicates

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

 translate_ics(Arg1, Arg2)

 translate_ics_files(Arg1, Arg2)

 download_ics(Arg1)

 parse_ics(Arg1, Arg2)

 parse_ics_string(Arg1, Arg2)

 add_var(Arg1, Arg2)