escape_chars to \x{...}

Sometimes I care deeply about the difference between \x{2603} and \x{e2}\x{98}\x{83}, even if my terminal doesn't.

So I added an "escape_chars" option that prints out \x{...} rather than the actual chars.  Takes options "none" (the default), "nonascii", "nonlatin1", or "all".

Hope you like it.

Mark.