function playNextPart(aScore) {
  aScore.currentPart++;
  if (aScore.currentPart >= aScore.parts.length) {
    aScore.scoreStep = 0;
    aScore.onended();
  } else {
    aScore.scoreStep = 0;
    aScore.parts[aScore.currentPart - 1].stop();
    aScore.parts[aScore.currentPart].start();
  }
}
Set the tempo for all parts in the score

 @method setBPM
 @for p5.Score
 @param {Number} BPM      Beats Per Minute
 @param {Number} rampTime Seconds from now