anchor.diff:     * */
     num speedY = 0;
   
  +  /**
  +   * Horizontal acceleration of the sprite.
  +   */
  +  num accelerationX = 0;
  +
  +  /**
  +   * Vertical acceleration of the sprite.
  +   */
  +  num accelerationY = 0;
  +
     StageXL.Vector mainDirection = new StageXL.Vector.zero();
   
     StageXL.Vector upDirection = new StageXL.Vector(0, -1);
  
positive.code:    * Direction can be: up/forward, down/backward, left, right
     */
    move(String direction) {
      //mainDirection = zeroVector;
      StageXL.Vector newDirection = mainDirection;
      switch (direction) {
        case 'up':
        case 'forward':
          newDirection += upDirection;
          break;
        case 'down':
        case 'backward':
          newDirection += downDirection;
          break;
        case 'left':
          newDirection += leftDirection;
          break;
        case 'right':
          newDirection += rightDirection;
          break;
      }
      if (newDirection.length > 1) {
        mainDirection = newDirection.scaleLength(1);
      } else {
  
negative.code:   }
  
    /**
     * Rotate the sprite and it's direction vectors in angles.
     */
    void rotateAngles(num angles) {
      rotateRadians(angles * (math.PI / 180));
  