Use http-Client over http-conduit and Style Changes

I updated to http-client as discussed here: https://github.com/evancz/elm-get/pull/9#issuecomment-34073251. Unfortunately pandoc/yaml have dependencies on conduit, so I don't think we're saving anything dependency-wise, but we are moving to newer/supported packages. This is the first commit.

The second commit adds -W and does non-controversial cleanup/type annotations.

The last commit stylizes imports like the style guides discussed here: https://github.com/evancz/Elm/issues/481 . Besides grouping imports by project this was entirely done by the command `find src -name "*.hs" | xargs stylish-haskell -i`. Seeing the before and after should give you a good idea of the kind of things this cleans up/produces. I think we should consider doing this across all Elm repos (at least periodically) to keep things clean, but I can also drop this commit from the pr if we decide against it.