Sound: ABC

Copperbox revision 74.

Updated the Abc parser and datatypes. The parser is now written with the applicative combinators. The datatypes have been made a bit more uniform, although this has only been done for the `data` definitions and not the `type` synonyms.

Added a pretty printing module and a top-level module.

Sound: ABC

Copperbox revision 73.

Renamed the `midifile` directory to `sound` and added a new sub-directory `Abc`, with a parser for Abc notation. This parser is a rough prototype at the moment.

Midi Lib

Copperbox revision 72.

Updated the file MidiWrite.hs so that it uses the changes to the the Midi datatypes (these changes should have gone in with yesterday's check-in - revision 71).

Added a demo - DemoTrack.hs - that outputs a scale using MidiWrite.

Midi Lib

Copperbox revision 71.

Replaced the Midi file library with a new version. The new version has error handling - undoubtedly a big plus. It is still a quite rough at the edges as I'm working out how much to use the combinators from Control.Applicative and how much to use my own combinators.