GDP: Markup command snippets - trial run

[Neil Puttock]

Graham,

I trust you've had a look at B.6 with my snippet additions; I think
you'll agree that it's not a pretty sight. :)

Several snippets are suffering from the PNG cropping bug (even in the
PDF output), so unless that can be fixed, it's probably preferable to
have musical examples for the majority of snippets (like Valentin's
rounded box example).

Regards,
Neil