ctor(options) {
    this.velocity = cc.p();
    this.targetVelocity = cc.p();
    this._super(options);
  }
*************************************************************************
 FXBoidSprite
 var FXBoidSprite = FXSprite
 FXBoidSprite.create()
 - this is (more or less) a puppet sprite that the flock sprite controls
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