Show compiler warnings in own section of Mix ExUnit Task output

[Havvy]

Right now the only way to see those compiler warnings is to actually look at the full output. It'd be useful if they were in their own section, possibly as a failing test?

[KronicDeth]

In Java the build output would go to the Build pane because the compilation is a distinct command, so I could do that: MIX_ENV=test mix compile first, put that in the build tab, but the usual way of tests are written, I don't think will actually catch the *.exs build output in that since they are only built in-memory when mix test is run.

Comparing it to Ruby in Rubymine, any warnings are just hidden in the full output as the plugin currently works.

So, no real obvious pattern from Java or Ruby.

I can check if the output from @JakeBecker's formatter is distinct for the compilation steps and capture them and put it in some separate output, but I think I'd need to add an option (off by default) to show compilation warnings as failed tests as otherwise people that are expected clean tests, but allow warnings will wonder why the test suite is failing.