Allow to configure custom onProgress

[xi]

see #194

This project is really, really helpful. The only thing I would like to change is the comand line output. However, I realize that you may need different output based on context. So I propose two tiny changes that would allow users to create custom progress reporters.

The first change is to allow to configure TestRunner.onProgress(). The second is to pass result in the jobComplete report. This makes it possible to output more details about the tests.

Example: This travis build used this Gruntfile.