changed barline length calculation
made THICKNESS an object property; added test case
- Clean up auto-beam tests
- Add test for auto beaming with inconsistent stem directions
- Add test for a beat group with an unbeamable note within it
Added a `maintain_stem_directions` config option to `generateBeams()`
Fixed bug where beaming over rests in a stem down group resulted in incorrect beam placement
Fixed auto-beaming edge case. Added a test to cover case.