New: scoreDef carries page measurement information
Fixed: clef changes are now enclosed in staffDefs within a milestone scoreDef

Fixed #1
Fixed: encoding ties as both elements and attributes was redundant

Now ties are only encoded as attributes on /note elements.
Fixed: Milestone clefs are now encoded in layer

This fix moves clef changes from scoreDefs to milestone clef elements that occur within layer.

Refs #1
Fixed: Remove trace