Wrong output for Unicode chars

For `\x{0660}` you get `<60>` and a warning `Character in 'H' format wrapped in unpack at /usr/local/share/perl/5.18.2/Data/Coloured.pm line 76.`

I replaced `unpack( "H*", $char )` with `( sprintf "%x", $chr )` and everything is fine.  I did a quick check with other input streams and it worked, but as the dist lacks of unittests, I can't say if it breaks anything.
