Since OM 2.0 connection of relationships happened during the object mapping operation
instead of aggregately at the end of the process. In this commit, we have introduced a lightweight
queue for deferring portions of the mapping operation until a larger aggregate mapping has completed.
The changes are as follows:
* Introduced RKMappingOperationQueue for queueing portions of mapping. This is a synchronous queue modeled off
of NSOperationQueue that does NOT use threading (for Core Data friendliness).
* RKObjectMappingOperation now has a RKMappingOperationQueue queue property that defaults to nil
* RKObjectMappingOperation instances built via RKObjectMapper will has a mapping operation queue
assigned to the property.
* If a queue is present, RKManagedObjectMappingOperation will use it to defer the connection of relationships.
* At the end of an RKObjectMapper process, the mapping operation queue used by all mapping operations created
during the process will be executed. This allows all relationships to be connected after all object creation
has completed.
The queue is general purpose, though currently only used for the connection of relationships.
Other changes include:
* Eliminated the RKObjectFactory protocol and implementations. Object mapping instances themselves are
now responsible for instantiating target objects for mapping.
* Introduced RKObjectAbstractMapping superclass for RKObjectMapping and RKObjectPolymorphicMapping.
* Updated example applications to use block object loaders (RKTwitter and RKTwitterCoreData)
* Refactored method signatures of RKObjectMapper, RKObjectMapping, and RKObjectMappingProvider to reflect the
existence of abstract mapping types. This was necessary to make polymorphic mappings integrate cleanly.
* Fixed overlap in RestKit error domains between network and object mapping. fixes#208
* 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
