Do not re-use stacktraces on IEx, closes #1486

This commit also cleans up error normalization throughout Elixir.
A test case changing compiler options should not be async
Fixed docs typos in recent commits
Merge pull request #1487 from jwarwick/typos

Fixed docs typos in recent commits
Update deps docs
Mix retriever should use the .app set at compile_path
Update new app docs
Fixed Kernel.match? example. Added formatting to Kernel docs.
Merge pull request #1492 from jwarwick/kernel_typo

Fixed Kernel.match? example. Added formatting to Kernel docs.
Update ExUnit.Assertions docs, closes #1493
Ensure environment is set before any task is executed, closes #1490
Group ExUnit.start calls into one, closes #1489
Add umbrella: true to supported deps options
Get rid of Mix.Tasks.IEx
Use %B on docs
Add mix cmd
Support --color option in ExUnit

The option can also be passed via mix, closes #1364
Update CHANGELOG
Allow defmacrocallback to be specified in Behaviour