function easeInOutBounce(t, b, c, d) {
    if (t < d/2) return easeInBounce (t*2, 0, c, d) * .5 + b;
    return easeOutBounce (t*2-d, 0, c, d) * .5 + c*.5 + b;
  }
@method easeInOutBounce
@memberOf fabric.util.ease