play(note, velocity = 0.1, secondsFromNow = 0, susTime = 1) {
    this.noteAttack(note, velocity, secondsFromNow);
    this.noteRelease(note, secondsFromNow + susTime);
  }
Play a note by triggering noteAttack and noteRelease with sustain time

 @method  play
 @for p5.PolySynth
 @param  {Number} [note] midi note to play (ranging from 0 to 127 - 60 being a middle C)
 @param  {Number} [velocity] velocity of the note to play (ranging from 0 to 1)
 @param  {Number} [secondsFromNow]  time from now (in seconds) at which to play
 @param  {Number} [sustainTime] time to sustain before releasing the envelope
 @example
 <div><code>
 let polySynth;

 function setup() {
   let cnv = createCanvas(100, 100);
   cnv.mousePressed(playSynth);
   background(220);
   text('click to play', 20, 20);

   polySynth = new p5.PolySynth();
 }

 function playSynth() {
   userStartAudio();

   // note duration (in seconds)
   let dur = 1.5;

   // time from now (in seconds)
   let time = 0;

   // velocity (volume, from 0 to 1)
   let vel = 0.1;

   // notes can overlap with each other
   polySynth.play('G2', vel, 0, dur);
   polySynth.play('C3', vel, time += 1/3, dur);
   polySynth.play('G3', vel, time += 1/3, dur);
 }
 </code></div>