Compare metadata on request and many other improvements/fixes

Changes since 2.0.1:
- Require music21 v9 (for several features/fixes) and converter21 v3 (for improved Humdrum and MEI import)
- Remove all checks for music21 features (they're all there in v9)
- compare Mordent/Trill/Turn better, to include ornament accidentals (newly supported in music21 v9)
- Compare metadata if requested (e.g. AllObjectsAndMetadata)
- compare StaffLayout.staffLines and StaffLayout.staffSize
- support tuplet.type = 'startStop'
- fix tie annotation
- finish tremolo annotation, both fingered and bowed
- compare rest positioning
- better comparison of RepeatBrackets (support .overrideDisplay)
- compare placement (above/below) of articulations and expressions (AllObjectsWithStyle)
- support comparison of StaffGroups as part of AllObjects. StaffGroup bracket shape is relegated to AllObjectsWithStyle.
- compare (and fill and transpose) Ottavas, maintaining accidental display status (newly possible in music21 v9)
- compare delayed turns (new in music21 v9)
- ignore redundant clefs during comparison
- compare tuplet number/bracket visibility and format (and placement if diffing WithStyle)