musicdiff v3.1.0 (note offsets and tuplets and lyrics)

Changes since 3.0.0:

Feature-level changes:
- Move lyrics diff from GeneralNotesOnly detail level to AllObjects detail level.
- Compare GeneralNote offsets (visually, this is horizontal position in measure).
- compare tuplet_info (num and numBase, num format/visibility, bracket visibility),
not just tuplet (start/continue/stop). This is technically a bugfix, but tuplet
comparisons were pretty much not working at all, so I'm calling it a new feature.
- Add py.typed, so clients can do mypy against musicdiff APIs.

Bugfixes:
Metadata:
- Contributor might not have any names. Deal with it.
- skip more metadata keys (that are specific to a particular file, so shouldn't
be compared against another file): 'EMD', 'EST', 'VTS', 'RLN', 'PUB'.
- html-unescape during annotation of metadata items.
Style:
- Ignore some style stuff we don't care about (e.g. absX/absY).
- Ignore fontSize, and regularize how 'bold' is represented.
Lyrics:
- Don't annotate lyric style if it is empty (hasStyleInformation could still be True).
- Consider lyric.syllabic == None and 'single' to be the same.
- Better comparison of lyrics, treat style.absoluteY as placement fallback when
placement is None.
- For lyrics, ignore placement=='below' and justify=='left', as equivalent to not
specifying.
- Ignore empty lyrics.
MetronomeMarks:
- Ignore playback-only MetronomeMarks (they're not marked invisible, but they are
not printed).
- Treat MetronomeMark with explicit number and no explicit text the same as one with no
explicit number and explicit text saying "x = NNN" (where x is a SMUFL note code
followed by 1-4 SMUFL dots). They are printed identically, so they are the same.
Barlines:
- no specified barline is the same as normal barline (at start and end of measure,
that is).
- ignore invisible ('none') barlines.
Other fixes:
- Fix crash when diff is visualized between note with accidental and unpitched note/rest
- Ignore redundant system and page breaks
- Grace vs Appoggiatura is more complex (in music21) than I thought.
- Skip over non-realized ChordSymbols (realized ChordSymbols get treated as Chords)
- Skip over StaffGroup that contains all the staves and has neither barTogether nor
symbol. Some file formats have one (MEI), and some file formats imply/don't need
it (MusicXML).