Throw out the custom test runner

First off, our custom test runner looks really ugly - which would be actually fine if it still had any value to it. I guess in the beginning it was used to distinguish in which area we still need a lot of work, however since we have to be at 100% success rate now to release any new version where it fails doesn't really matter anymore.

The main problem with the custom runner however is that it doesn't handle all edge-cases of nodeunit. The issue which crops up most in that regard are async tests which fail and then don't call ```t.done()```. In the default nodeunit runner this leads to a failed test which reports the missing done call, in the custom runner, this just leads to an abort (with a success exit code even, if I remember correctly, which makes it even worse when using it with travis).

It also introduces some custom code which has to be maintained every time some change is made.

Does the custom runner still serve any purpose or can we look into ripping it out and using the default nodeunit command?