Need to exec something on .done() without having to write a custom reporter.

The built-in reporters work great. But I need to be able to run something on `.done()` and I don't see any way of doing that other than to write my own reporter. It would be painful to have to write and maintain a custom reporter just for the sake of adding in some "execute this callback when all done" functionality, when I don't want to change any other behavior.

Can you add in the ability to do this?