Thoughts on naming this `-rac_signalForKey:` to keep consistency with other naming conventions like the previous name of this (`-rac_channelTerminalForKey:`) or [UIControl+RAC's `-rac_signalForControlEvents:`](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/3.0-development/ReactiveCocoaFramework/ReactiveCocoa/UIControl%2BRACSupport.h#L17)?