* Builds on work started by @OpenFibers.
* Should eliminate all cache warnings.
* Added FileMD5Hash library for efficiently computing MD5 for files
* Extended RKParams to return composite MD5 for all attachments
* Implemented MD5 method on each RKParamsAttachment instance
* Updated RKRequest to utilize new MD5 sums and enabled cache keys for RKParams
* 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
* Factored out display of alerts into RKAlert interface that hides the differences between UIKit and OS X Cocoa.
* Added macosx to supported platforms to enable build on OS X.
* Configured project to use conditional architectures to enable building on OS X and iOS from the same targets.
* Implemented a bare-bones OS X example app.
* Create `rake build` task for building RestKit against iOS and OS X SDK for quick testing.
