Undocumented predicates

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

 add_suffix(Arg1, Arg2, Arg3)

 is_newer(Arg1, Arg2)

 line_atom(Arg1, Arg2)

 save_to_file(Arg1, Arg2)

 term_to_file(Arg1, Arg2)

 with_output_to_file(Arg1, Arg2)