* Migrated the caches to return `NSSet` to eliminate duplicate objects when your cache keys overlap
* Introduced new recursive strategy for building cache keys in `RKInMemoryManagedObjectCache`
* Added support for array cache key values in `RKFetchRequestManagedObjectCache`
* Re-enabled a slew of tests that were disabled during 0.20 development
* Replaces primary key with `RKEntityIdentifier`
* Add support for use of compound keys for object identification
* Refactor `RKConnectionMapping` to `RKConnectionDescription` and add support for connecting with multiple attributes
* Clarify naming of representation key methods to better match naming conventions
* Add type transformation support for object identification
* Greatly expand test coverage for object identification
* Drop the `NSEntityDescription` category
* Simplify the `RKManagedObjectCaching` protocol
* Add compound key support to the Fetch Request and In Memory Cache implementations
* Replace Kiwi with Specta for tests where contexts are helpful for organization
* Rename `defaultValueForMissingAttribute` to `defaultValueForAttribute`
* Reworked execution of relationship connection operations to use dependencies instead of queue suspension.
* Migrates responsibility for connecting relationships from `RKManagedObjectRequestOperation` into `RKManagedObjectResponseMapperOperation`. This ensures that you get a mapped and connected object graph back from the response mapper if you are using it outside of a request operation.
* Add `parentOperation` to managed object mapping data source to establish dependencies.
