Bala

Copperbox revision 154.

A rethink of attributes for SymLilyPond and SymAbc. Attributes are no longer a 'continuation' (repr (a ctx) -> repr (a ctx)) over an element, they are now just elements. To establish that one element is a attribute of another element there is a empty class:

class Attribute elt attrib

Declaring instances of Attribute will put an attribute relation on the two types, then attribution can be done with the SymAttr class or its helper (#@).

Pleasantly this is both simpler and more useful that the continuation version.