Upload build logs from Hydra to Hackage

[peti]

Hackage allows users to upload build logs that indicate whether a package was compiled successfully or not (and what exactly the problems were, if any). It would be nice to upload build reports from our Hydra builds. I looked at http://hackage.haskell.org/api#reports-core, but frankly didn't manage to upload anything because the documentation isn't terribly detailed.