NR 2.9 world music

[Graham Percival]

I've added NR 2.9 "World music".  Currently it'll only contain
Arabic music, but now it's there, if somebody wanted to write
about special tricks for 12th century Sweedish folk songs or
African drumming, the space is there.

If anybody really objects to "World music", feel free to suggest
alternatives.  I don't want to get into a big debate about the
name; if somebody really wants the name to be something else, I'm
open to changing it.  But let's not waste too much time on the name.

Cheers,
- Graham