Undocumented predicates

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

 pchar_upper(Arg1, Arg2)

 pchar_lower(Arg1, Arg2)

 pchar_type(Arg1, Arg2)

 pchar_code(Arg1, Arg2)

 pchar_hex2(Arg1, Arg2)