NSDateFormatters, added a preferredDateFormatter for use when serializing dates to strings,
replaced the use of the description method for date encoding to strings with invocation of the
preferredDateFormatter, added new attribute transformation strategy from NSDate -> NSString properties
(also using the preferred date formatter), and provided customization support for date handling globally
and on a per-mapping basis. closes#200, closes#313, closes#309, closes#308
* 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
Introduces four modes for handling background requests:
* RKRequestBackgroundPolicyNone - The default behavior replicating pre-background behavior. No special action is taken with regards to backgrounding.
* RKRequestBackgroundPolicyCancel - On transition to the background, requests with this policy set will be cancelled automatically and the delegate informed.
* RKRequestBackgroundPolicyContinue - Requests with this policy will be continued in the background after the app has been transitioned.
* RKRequestBackgroundPolicyRequeue - Requests with this policy will be cancelled and then immediately placed onto the queue for processing the next time the app is returned to the foreground.
