Update version number.
Display/use keyboard shortcuts for the correct drum.

Fixes #274.
A little light refactoring, thinking towards #275
Check that sound is possible; disable gracefully if not.

Closes #272.
Closes #276.
Closes #277.
Make sure MIDI is always closed properly.

Closes #278.
Cosmetic.
Fix failing tests.

Working towards #90.
Fully test NotePosition objects.

Unit tests for #90.
Unit tests for Drum module.
Only need to call main once!
Remove unused method.
Remove unused import.
Unit tests for DrumKit module.
Refactor checking that drums have appropriate note heads.
A NoteDictionary is private to this module.
Add unit tests for empty measure tests, and make that test quicker.
Some unit tests for measures.
Make measure clearing more efficient.
Only reformat when necessary. Refactor hash checking into separate command.

Closes #281
Neater way to define undo checks.