Ported project and tests to Xcode 4 / iOS 6

This library was originally written using the Xcode 5 (DP5) IDE, and targeted for iOS 7; tests were originally on XCTest. This version should build correctly on Xcode 4.6, for iOS 6.1; tests should pass using OCUnit. Once iOS 7 and Xcode 5 are publicly released, those versions will become master.