A bunch of internal canges as well as API changes.

 Authentication changed to
    +(void)SH_authenticateWithLoginViewControllerBlock:SHGameViewControllerBlock)theLoginViewControllerBlock
    didLoginBlock:(SHGameCompletionBlock)theLoginBlock
    didLogoutBlock:(SHGameCompletionBlock)theLogoutBlock
    withErrorBlock:(SHGameErrorBlock)theErrorBlock;

Caching and requests
    will write cache
      GKTurnedBasedMatch SH_requestMatchesAndFriendsWithBlock:
      GKTurnedBasedMatch SH_requestPlayersWithBlock:
      GKLocalPlayer      SH_requestFriendsWithBlock:

    write/read cache
      GKTurnedBasedMatch  SH_requestMatchesWithBlock:
      GKTurnedBasedMatch  handleTurnEventForMatch:
      GKaTurnedBasedMatch handleMatchEnded:
Merge pull request #2001 from seivan/feature/SHGameCenter

0.3.0 - added caching to all requests. Changed authentication API.