Merge pull request #167 from kicktheken/master

Fix textBaseline 'top' and 'middle'
Cosmetics
Always try GameCenter auth when calling softAuthenticate for the very first time
Invoke callback with error if GameCenter soft auth was skipped
Reflect GameCenter changes in README
Typo
Fix #156 - prevent GameCenter views from attempting to show twice
Cosmetics: removed obsolete TODOs