Update to latest stack version and fix warnings.

[cdepillabout]

This PR includes a couple different changes:

• Updates the stack version from 3.20 to 6.11.
• Removes any support for ghc versions less than 7.10.
  • It looks like there was originally support for 7.8, but origin/master currently does not compile on 7.8, so everything about 7.8 was removed.
• Gets rid of all compiler warnings.
• Adds a .travis.yml. You can checkout the tests here. It's currently being tested on a couple recent versions of stackage, along with raw cabal. Everything is passing (other than GHC HEAD).
  • The .travis.yml was adapted from here.
• Adds a simple README.md.

[cdepillabout]

I think I'm going to send a could more PRs over the next week. I might also want the other open PR merged in.

@meteficha If you wanted to make me a member for fb (just like ig), I could go ahead a do a new release when I get my changes in.

[bitc]

This should be bumped up to aeson >= 0.7 since that is when the function encodeToTextBuilder was introduced (which you use in this PR)

• https://hackage.haskell.org/package/aeson-0.6.2.1/docs/Data-Aeson-Encode.html
• https://hackage.haskell.org/package/aeson-0.7.0.0/docs/Data-Aeson-Encode.html

[bitc]

@meteficha +1 to the above for giving @cdepillabout access to do a release :)

[cdepillabout]

@bitc Thanks for the heads-up! I've bumped the aeson dependency.