ochre-lang

Copperbox revision 3152.

I've added some extra syntax for instrument definitions before I start work on the translation from top-level syntax to the intermediate representation.

Instrument definitions should be thought of as (named) classes that are instantiated by an orchestra definition that supplies their instrument number (orchestra definitions are still to add to the syntax). Once I have class-like objects I hope implement something like traits to compose class fragments, modularizing the definition of instruments.