Rewrite .travis.yml to use containers and stack.
Rewrite .travis.yml to use containers and stack.

This should make the build faster and more reliable,
and hopefully ressurect the test suite.

sumitsahrawat/IHaskell,thomasjm/IHaskell,gibiansky/IHaskell,gibiansky/IHaskell,gibiansky/IHaskell,sumitsahrawat/IHaskell,franklx/IHaskell,thomasjm/IHaskell,franklx/IHaskell,sumitsahrawat/IHaskell,thomasjm/IHaskell,franklx/IHaskell,franklx/IHaskell,thomasjm/IHaskell