Added generic driver

Yeti should have a basic, generic driver for any apps that wish to submit test results, but not hack into Yeti's `inject.js`.  Here's a patch that adds just that.  If you have any ideas for something other than a global function to submit results, lemme know.  I figured it would be ideal to not be library-dependent for something generic.

Ideally, I think there should be a global `Yeti` object with a `submitResults` or `results` event listener, so
    
    Yeti.submitResults(results);
or

    Yeti.emit('results', results);

But this works until more thought can be put into it.