* 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
* Cleaned up remaining warnings about if (self = [super init])
* RKParamsExample - Highlights multi-part uploads
* RKRequestQueueExample - Working with the request queue
* RKBackgroundRequestExample - Examples of using the background policies for backgrounding requests
* RKReachabilityExample - Shows how to work with the reachability observer
* RKRelationshipMappingExample - Shows how to map related objects from JSON into an object graph
* RKCoreDataExample - Shows the basics of using RestKit's Core Data examples
Also rearranged dispatch of RKRequest delegate method for didStartLoad: to ensure requeue callbacks get invoked in a timely manner. refs #62
