* Introduces RKRequestCache for cacheing responses (supports ETag conditional GET, use cache if available, use cache on error, etc.) closes#75
* Updates to Three20 layer to eliminate need for intermediary TTTableItem classes closes#76
* Fixes to ensure iOS 3.x compatability:
* Switched compiler to Clang
* Updated conditional checks for UIBackgroundTask symbols to ensure runtime safety on iOS 3.x
* Removed unnecessary linkage against UIKit and CoreFoundation from library targets
* Fix for issue where RKRequest objects could become stuck in infinite loop within RKRequestQueue loadNextInQueue if you start
a request and then cancel immediately. On cancel only decrement loadCount if the request has start loading. refs #122
* Removed RestKit from inheritance hierarchy
* Mappings are implemented as concrete classes
* Mapper is much more flexible & powerful
* Much more robust error handling
* Serialization is reimplemented as an object mapping operation
* Added ability to serialize to JSON natively
* Reworked Core Data integration
* Simplified the codebase substantially
* Cleaned up various mismatches in method signatures that were preventing documentation generation
* Removed naked ampersands from comments as they cause XML parser failures during docset generation via appledoc
