Removed ChordAgent.
Renamed GraceAgent to GraceMaker.
Renamed PitchAgent to PitchMaker.
Renamed AttachmentAgent to AttachmentMaker.
All makers now inherit from AbjadValueObject.
Removed unused ConsortObject.

Use AbjadValueObject instead.
Score iteration now uses SegmentMaker._process_score().
Removed three .iterate_score() methods.
Added four parameterized tests for copying, hashing and pickling.
All classes now pass all parameterized tests.
Renamed PitchCurve to BreakPointFunction.
Renamed AttachmentSpecifier to AttachmentExpression.
Renamed PitchMaker to PitchClassPitchMaker.

There will certainly be at least two, if not three kinds of pitch makers:

    - via pitch-class and break-point octavation
    - via harmonic field and break-point lookup
    - via "percussion pitch" sequence