Sound = function() {
  // Setup the shared Howl.
  this.sound = new Howl({
    src: ['./assets/sprite.webm', './assets/sprite.mp3'],
    sprite: {
      lightning: [2000, 4147],
      rain: [8000, 9962, true],
      thunder: [19000, 13858],
      music: [34000, 31994, true]
    },
    volume: 0
  });

  // Begin playing background sounds.
  this.rain();
  this.thunder();
}
Setup and control all of the game's audio.