This has been a long time coming, but it's still not perfect. Basically
I'm trying to reset the entire environment as much as possible so that
each spec runs in a clean room. Mostly in this commit Firefox is being
killed and restarted for every spec, which has made a lot of
improvements.
After moving to Tcell and implementing its screen diff updates, we can
no longer watch STDOUT to get frames during integration tests. Instead
we need to use Tcell's SimulationScreen and which has a GetContents()
method. This is actually also a much more robust way of being able to
see what Browsh actually outputs during testing.