add cocos2d::Vector constructor with initializer_list

cocos2d::Vector is now able to create with initializer_list like this:
```cpp
  auto *cache = cocos2d::SpriteFrameCache::getInstance();
  
  cocos2d::Vector<cocos2d::SpriteFrame*> frame{
      cache->getSpriteFrameByName("foo"),
      cache->getSpriteFrameByName("bar"),
      cache->getSpriteFrameByName("buz"),
      // ...
  };
  
  mySprite->setSpriteFrame(frame.at(0));
```