Fix auto-stem calculation, use same function for calculating beam group stem directions in .generateBeams() and autoStem on construction, fix TabNote bug where the stem direction was being always forced UP on construction, add/fix tests
Change integer stem directions to constants, swap incorrect test names for .dotsAndBeamsUp/Down
Merge pull request #253 from Silverwolf90/fix/auto-stemming

Fix auto-stem calculations
Refactor ModifierContext, move formatters for Dots, Accidentals,
FretHandFinger, GraceNoteGroup, and StaveNote into their respective
classes.
Moved Stroke, StringNumber, and Articulation modifier formatting into their
respective classes.
Refactored the rest of the modifier formatting. Also refactored
getCategory for all modifiers.
Create PREFORMATTERS and POSTFORMATTERS arrays to simplify modifier creation.