improviso lyp package

This is a packaging of the improviso font packages and the lilyjazz stylesheet for use with the lyp package manager.

Most of the contents is just a rearrangement of Steve Lacy's (@slacy) https://github.com/OpenLilyPondFonts/improviso repository (which itself is based on Abraham Lee's font and lilypond work) to conform to lyp packing standards.

The only added files are:

• package.ly, the lyp packaging root.
• jazzchords_test.ly, a test sheet for a wide variety of jazz chords.
• morejazz.ily, a number of tweaks to the chord name display, notably
  • Using a triangle instead of "M" for major 7th chords.
  • Adding a few more exotic chord combinations.
  • Defining stacked alterations in a way that is more robust to font size variations.

To restore the chord naming in the original package, add \set chordNameExceptions = #JazzChords in your file.