API: Clean up and internationalize pretty-printed output
The syntax highlighting applied to the XML format is not all that great,
and applying it to other formats is just wrong. Instead of doing it
ourselves, let's just add a hook and let Extension:SyntaxHighlight_GeSHi
do it for us.
But for that to work, we have to add RL support to the pretty-printed
output, which means OutputPage. At the same time, lets internationalize