Upgrade to lastest ExUnit changes and some smaller changes

I wanted to use amrita yesterday with the latest elixir bits and noticed that (at least on my machine) amrita was breaking under 0.12.

I looked into the elixir repo and apparently the Elixir.ExUnit.TestCase and Elixir.ExUnit.Test records have changed (together with some functions that work on them). There's no 'failure' property any more. It's called 'state' now and it's used differently now.

I updated all locations in the runner and the formatters to the latest changes so that they run again. I also updated to the latest ex_doc version and excluded the new _build directory from git.