Support Haddock documentation for generated code

[typedbyte]

As far as I know, it is currently not possible to include Haddock documentation in the code generated by Template Haskell (see the related ticket). As a consequence, declarations generated by functions like makeTaggedEffect, makeTagger and makeUntagged currently have no documentation. This is no big problem, since the documentation is usually attached to the tagged counterparts of the generated declarations, but it is a situation that can be improved nonetheless.

For single declarations generated by makeUntagged, one can currently document them like this ...

-- | The untagged version of 'runLocalFileSystem''.
makeUntagged ['runLocalFileSystem']

... but in the future, I would like to copy the documentation over from the original tagged declarations, which means that no manual handiwork is needed. Guess we have to wait until the related ticket is resolved.