Fix beamlet pointing wrong way in tuplets (issue 11).

Fix beamlet pointing wrong way in tuplets (issue 11).

Add data structure to capture the tuplet structure.

Make beaming reflect subdivisions.

Eliminate rule to force minimum beamlets by combining all beams,
and replace it with rule to make beamlets point toward complete
beats (high rhythmic importance).

Add regression tests.

Adjust to handle beats properly for subdivision

Add regression test for beamlets pointing toward beats