Minor doc fixes to GHC.Generics
Minor doc fixes to GHC.Generics

This adds @since annotations and fixes a couple of Haddock formatting
errors.

olsner/ghc,snoyberg/ghc,mettekou/ghc,sdiehl/ghc,mettekou/ghc,sgillespie/ghc,tjakway/ghcjvm,snoyberg/ghc,vikraman/ghc,sgillespie/ghc,mcschroeder/ghc,sgillespie/ghc,ezyang/ghc,sdiehl/ghc,oldmanmike/ghc,olsner/ghc,nushio3/ghc,mcschroeder/ghc,sgillespie/ghc,sdiehl/ghc,vTurbine/ghc,vTurbine/ghc,sgillespie/ghc,snoyberg/ghc,nushio3/ghc,olsner/ghc,vikraman/ghc,oldmanmike/ghc,tjakway/ghcjvm,vikraman/ghc,vTurbine/ghc,nushio3/ghc,vTurbine/ghc,snoyberg/ghc,mcschroeder/ghc,oldmanmike/ghc,nushio3/ghc,tjakway/ghcjvm,snoyberg/ghc,tjakway/ghcjvm,ezyang/ghc,ezyang/ghc,mcschroeder/ghc,sdiehl/ghc,shlevy/ghc,tjakway/ghcjvm,ezyang/ghc,sgillespie/ghc,snoyberg/ghc,vTurbine/ghc,mcschroeder/ghc,vTurbine/ghc,vTurbine/ghc,mettekou/ghc,oldmanmike/ghc,mettekou/ghc,tjakway/ghcjvm,ezyang/ghc,mcschroeder/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,snoyberg/ghc,oldmanmike/ghc,sdiehl/ghc,olsner/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,olsner/ghc,vikraman/ghc,nushio3/ghc,oldmanmike/ghc,vikraman/ghc,vikraman/ghc,olsner/ghc,sgillespie/ghc,tjakway/ghcjvm,nushio3/ghc,oldmanmike/ghc,shlevy/ghc,shlevy/ghc,mettekou/ghc,shlevy/ghc,ezyang/ghc,mcschroeder/ghc,shlevy/ghc,vikraman/ghc,mettekou/ghc,nushio3/ghc,sdiehl/ghc