Mullein

Copperbox revision 749.

This is a checkpoint commit before I change the code that works on the glyph types again. I think I can now the rewriteDuration and rewritePitch functions usefully polymorphic by following the example of monad transformer constructor classes.

The monad transformers have there arguments carefully ordered so they have made instances of the important classes - the answer type of the transformer is always the last argument (satisfying the signature of Monad) and the monad parameter m is always the next to last (satisfying the signature of MonadTrans).