Add hcVersion to get version of a particular compiler flavor

This resolves the error message saying the compiler is version 0.1.0 but haddock needs version 7.8.3.  It adds the hcVersion function and modifies Haddock.hs to use hcVersion GHC instead of compilerVersion.  Luite, I think you said you were working on this stuff, so this may duplicate some change you are working on.