Extended show() with **kwargs.

You can now do ...

    >>> maker = rhythmmakertools.NoteRhythmMaker()
    >>> divisions = 4 * [(1, 16)]
    >>> show(maker, divisions=divisions)

... because RhythmMaker.__illustrate__(divisions=None) knows what to do with a
divisions=None keyword.

Other __illustrate__() methods can be extended the same way.

Note that this usage of show() does not yet work in the docs. Probably because
of the special handling needed there to process calls to show().