Lexing character literals in H98

[Sven Panne]

Yet another H98 question, this time regarding the module Char: Is it
a deliberate design decision that readLitChar handles decimal, octal,
and hex escapes, but lexLitChar handles only decimal ones? It looks
more like an oversight to me...

Another question is if the uppercase variants '\O...' and '\X...'
should be forbidden explicitly. Current implementations seem to differ
in this aspect.

Cheers,
     S.