fixes #2 & modernizes codebase

All commits here but the last update the codebase for: 

 * Xcode 5.1.1
 * 10.9 SDK & 10.4 deployment
 * tabs `->` spaces for indentation
 * migrate 10.6-deprecated API (`AudioHardwareGetProperty -> AudioObjectGetPropertyData`, etc.)
 * fix some compiler warnings

Then, the last commit fixes #2 and allows for an audio device (e.g., `Display Audio`) to serve as both an input and an output option if appropriate.