Made IncisedRhythmMaker more robust.

You can now initializer IncisedRhythmMaker completely empty ...

    maker = rhythmmakertools.IncisedRhythmMaker()

... and it will work.

The output is identical to NoteRhythmMaker.

Useful as a trivial stage of configuration early in the process of building up
a more complex configuration.