getRotateTowardsAngle(vec, center, angle) {
    let tmp = this.clone();
    tmp.rotateAround(angle, center);
    let distSqA = tmp.distanceSq(vec);
    tmp.rotateAround(-2.0 * angle, center);
    let distSqB = tmp.distanceSq(vec);

    if (distSqB > distSqA) {
      return angle;
    } else {
      return -angle;
    }
  }
Returns the angle in radians used to rotate this vector towards a given vector.

@param {Vector2} vec The vector this one is rotated towards to.
@param {Vector2} center The rotational center.
@param {Number} angle The angle by which to rotate.
@returns {Number} The angle in radians.