删除了原prom中的GKMatchmakerViewController分类，修正了6.0设备上crash的问题
GameCenterManager is a simple singleton class that has methods for authentication, leaderboard score reporting, achievement reporting, as well as achievement and leaderboard view displaying! There is even a category included for making a GKMatchmakerViewController landscape! Note that your project must link against the GameCenter framework.
Usage.m is a file showing the usage of this class, this is NOT a proper class implementation.
There is no attribution required but is greatly appreciated!
Thanks for downloading, Santiago
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(Uses Matt Gallagher's SynthesizeSingleton macro, http://cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html)