Add more derivations

[ndmitchell]

Add Data/Typeable to the definitions without exception - they are very handy for SYB style stuff (which HLint does a lot of).

If RType will always be an enum (as it looks plausible) think about also adding Enum and Bounded, which gives you the handy [minBound..maxBound] to loop over all RTypes, but that one is less important, and arguably there's little chance to by polymorphic over the RType, so it might not make sense.