Bala

Copperbox revisions 215 & 216.

Revision 215 - a substantial amount of changes as I'm working towards making the Perform modules a standalone library. Particular I've added minimal data types for pitch and duration - this has simplified the internals of the library quite a lot as it is no longer trying to be polymorphic on external pitch and duration representations.

Also I've move the Score representation from Format into Perform, at some point I'll do the same with the pretty printers for Abc and LilyPond in Format/Output. The Midi library should probably be made into a separate package too.

Revision 216 - deletes some of the files that that revision 215 made redundant. For the time being there is still a copy of the Score library in Format but this will go when I've checked there are no references to it.