Pitch objects can now be instantiated from other Pitch objects.
Improved consonance-detection in OffsetTree.
Implemented inversion-equivalent interval class set detection in ChordReducer.
Integrated interval-class-set detection in ChordReducer.

ChordReducer can now collapse arpeggiated seventh chords which lack either
their third or their fifth.

There are certainly some false positives, but in general, this does a better
job simplifying things than before.