cocos2dx SpriteBatchNode 精灵的渲染优化类

用处是减少对精灵的渲染次数，用法如下

1     SpriteFrameCache::getInstance()->addSpriteFramesWithFile("person.plist");
2     SpriteBatchNode *node = SpriteBatchNode::create("person.png");
3     bg->addChild(node);
4
5     SpriteFrame *frame = SpriteFrameCache::getInstance()->getSpriteFrameByName("navigationbar_back.png");
6     Sprite *spt1 = Sprite::createWithSpriteFrame(frame);
7
8     node->addChild(spt1);