code: function rotatePoint(point, degrees) {
      // TODO use existing function
      var angle = Math.PI / 180 * degrees;
      point.x = point.x * Math.cos(angle) - point.y * Math.sin(angle);
      point.y = point.x * Math.sin(angle) + point.y * Math.cos(angle);
      return point;
  }
docs: Rotation: rotate a point about another point by some number of degrees