There's currently a known issue for appledoc (https://github.com/tomaz/appledoc/issues/147) that causes it to fall over when it encounters a method declaration in an implementation that is missing a type (even if its in the header file). While this is valid Objective-C, lets update this to allow appledoc to go on its merry little way.
* Fix 1 declaration relating to atKeyPath: in RKObjectMapper.m
* Fix 2 declarations relating to atKeyPath: in RKObjectMapper_Private.h
* Fix 1 declaration relating to atKeyPath: in RKObjectMappingOperation.m
All declarations were changed to declare keyPath as an (NSString *).