Undocumented predicates

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

 read_file_to_string(Arg1, Arg2)

 atomic_constant_list(Arg1, Arg2, Arg3)

 atomic_constant(Arg1, Arg2, Arg3)

 elementList(Arg1, Arg2, Arg3)

 drop_whites(Arg1, Arg2)

 drop_comments(Arg1, Arg2)

 opening_parenthesis(Arg1, Arg2)

 term(Arg1, Arg2, Arg3)

 term_list(Arg1, Arg2, Arg3)

 comma(Arg1, Arg2)

 time(Arg1, Arg2, Arg3)

 closing_parenthesis(Arg1, Arg2)

 funct(Arg1, Arg2, Arg3)

 number(Arg1, Arg2, Arg3)

 variable(Arg1, Arg2, Arg3)

 full_stop(Arg1, Arg2)