PerGens, generalized note names and accidentals

• New: Add pergen module
  • Find generalized accidentals
  • Find generalized note names
• Improvement: Notes are rendered in a more consistent and compact way
  • ▲Eb / ▲F# is now rendered as (Eb/F#)[1]
  • #/b always means +/- one sharpness step. If the sharpness is negative -/+ is printed instead of #/b