extended RKObjectMappingMatcher capabilities with a RKKeyPathClassObject...

...MappingMatcher class
to be honest I think it's right as it is.

instancetype is already defined on the static methods, but the init methods one for each class are returning id.

can't see anything wrong with it.

I think if you have a look at that file from Xcode instead that on the github diff you will understand what I mean.