I modeled this after [NSData+RACSupport](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/ReactiveCocoaFramework/ReactiveCocoa/NSData%2BRACSupport.m) and [NSFileHandle+RACSupport](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/master/ReactiveCocoaFramework/ReactiveCocoa/NSFileHandle%2BRACSupport.m).

You know I'm certainly a fan of cold signals, but I don't want to create inconsistent behavior.