Implement long-term Stackage strategy

[dogonthehorizon]

As soon as some out-of-bounds packages got added to Stackage the build failed for hal and it was removed from nightly :(

In 0.1.2 we added pvp-bounds: both-revision so that stack sdist && stack upload don't initially set bounds and we don't have to spend as much time fixing build errors.

That said, we still need to add more LTS/nightly versions of the lib to upcoming Travis builds so we make sure we're aware of any changes as early as possible.

[JackKelly-Bellroy]

Is this relevant? CI appears to have included stackage nightly for a while.

[IamfromSpace]

CI appears to have included stackage nightly for a while.

Yep, wrangling envy was the final piece of getting this in order. From here it's ready to go to get back into Stackage.

[JackKelly-Bellroy]

I am not familiar with the stackage ecosystem at all, so I'll leave that one to you.

[IamfromSpace]

Absolutely, Been a bit pressed for time lately, but it's on my list. I'm excited to get it dropped from the extra-deps of a few projects :)