Log Message:
py-music21: update to 6.7.0

Change log:

    Important bug fix: if you’ve had trouble loading music21 with an \ 
“importlib” error, this is fixed.
    Composite lyrics changes to the implementation in 6.5: multiple syllables on \ 
one note in a single verse (like in Italian, “Il bianco e dolce cigno”) now \ 
are imported to MusicXML property, stored in a Lyric.components object, and \ 
export to MusicXML properly.
    Lyrics searching finds all lyrics in all verses (and composite lyrics too)
    More major improvements to piano staff imports (thanks to Jacob Tyler Walls \ 
= JTW)
    RomanNumeral.isMixture() shows whether a chord is borrowed from the other \ 
mode (Mark Gotham)
    Several improvements in chord symbols (JTW + Alexandre Papadopoulos)
    More improvements to finding instrument names from MIDI (JTW)
    Duration marks in chords in ABC import properly (Marian Schultz)
    Documentation improvements.
    MusicXML parse failures now more often give the part and measure context (JTW)
    Substantial bug fixes in Stream.setElementOffset. Adds a new \ 
Stream.coreSetElementOffset for the dangerous but super fast version, and makes \ 
the original version safer. (JTW)
    Bug fixes in MEI articulations (heinzer) and accidentals (JTW)
    Bug fixes in external tools in windows including spaces (JTW)
    Channels handle better in MIDI (bearpelican)
    Humdrum files with positioned rests no longer crash (Phil Kirlin)
    OctaveRepeatingScale and CyclicalScale now usable as abstract classes (JTW)
    Articulations and expressions musicxml does not support are exported as (JTW)
    Better support for .musicxml as a file name within compressed .mxl files.
    Beaming in pickup measures is fixed.
    Stem directions can now be set automatically to coincide with beam groups. \ 
This is very useful if you are creating your own notation from scratch (as in \ 
VexFlow output; m21j gets the same routines)
    Spanner endHeight and startHeight are processed correctly (JTW)
    NoChord objects (in Chord Symbols) now retain their text (like “N.C.”) \ 
in more situations (JTW)
    All NotRest objects get a .pitches function – a small thing, but will be \ 
helpful in the future.