majalan

Copperbox revision 2962.

I've reworked the Score objects to use a Writer or Writer+State monad as their base.

Previously each object was written as a monad from scratch, but I wanted to add an EventList that builds an Impulse Map. Because Impulse Map is a finite map (efficient insert, bad concatenation) it doesn't make a good accumulator as a Writer - it is better to thread a single map as State. Hence I need new primitives to build accumulators.