* Enable evaluation blocks to return an NSError describing the failure
* Align all RKAttributeMapping references to RKPropertyMapping
* Cleanup docs
* Add `RKMappingTestExpectationTestCondition` macro for succinctly implementing mapping test evaluation blocks
* Clean up descriptions for better output from Kiwi
* Added error domain and codes specific for the mapper
* Migrated from using an NSString to real NSError objects
* Toned down the verbosity of error output for readability
* Cleaned up comment formatting
* Changed RKAttributeMapping to RKPropertyMapping for better alignment with the realities of the data model