code: function pitchClass (p) {
    if (!p) return null
    else if (Array.isArray(p)) return [p[0], p[1], null]
    p = asPitch.parse(p)
    return p ? asPitch.stringify(pitchClass(p)) : null
  }
docs: Get the pitch class (pitch name without octaves) from a pitch
  
  @param {String|Array} pitch - the pitch to get the pitchClass number from
  @return {String} the pitch class
  
  @example
  pitch.pitchClass('a4') // => 'A'
  pitch.pitchClass('ab') // => 'Ab'
  pitch.pitchClass('cx2') // => 'C##'