deprecated Audio Session API in iOS 7.0

https://developer.apple.com/library/ios/releasenotes/General/WhatsNewIniOS/Articles/iOS7.html

Audio Session API in the Audio Toolbox framework are deprecated as of iOS 7.0.  I received several compiler warnings regarding this, although it appears not to affect functionality on iOS7.  Per Apple, "Apps should use the AVAudioSession class in the AV Foundation framework instead."
