Xcode 6 support

Also renamed `-and`, `-or`, and `-not` for Swift compatibility. Fixes #1366.

The unit tests don't currently build, because Specta/Expecta haven't yet been updated for Xcode 6.
That's really shitty. :confused: 

Last I heard, this was a bug in the compiler that might get fixed, though? Does anyone know if that's still the case?

@ReactiveCocoa/reactivecocoa