Support mtl-2.3

[sjakobi]

TODO:

• Run tests

Upstream issues:

• Compatibility with mtl-2.3 haskell/parsec#148
• Support mtl-2.3-rc3 UnkindPartition/tasty#318

[andreasabel]

Seems like this is warranted by haskell/mtl#117. If you prefer releasing quickly, would you mind adding a lower bound? transformers >= 0.4 is needed for ExceptT, AFAICS.

[andreasabel]

Please add lb for transformers. I fear @hvr's wrath if not all dependencies have lower and upper bounds. ;-)

[andreasabel]

@sjakobi : I invited you to collaborate. If you accept, I can also add you to the hackage uploaders.
I do not have much interest in HsYAML myself, but it is relevant to e.g. haskell-ci and cabal-dev-scripts (in GHC and cabal). So it is needed still by the community.

[andreasabel]

Released as 0.2.1.1

[sjakobi]

Thanks for the invitation and the release, @andreasabel! :) I have accepted the invitation.

For now, I'm not planning on doing very much in this repo. But since dhall-yaml depends on HsYAML I have an interest in keeping the lights on.