code: function getAngle(touch1, touch2) {
      var x = touch2.clientX - touch1.clientX,
          y = touch2.clientY - touch1.clientY;
  
      return Math.atan2(y, x) * 180 / Math.PI;
    }
docs: calculate the angle between two coordinates
  @param {Touch} touch1
  @param {Touch} touch2
  @return {Number} angle