Setup a visual QA test suite

[mojavelinux]

For our sanity, we need a visual QA test suite so that we know when a change to the stylesheet definitions, esp the core asciidoc component, causes unanticipated side effects.

I created a very rough list of the stylesheet QA we do while we were prepping the 1.5.0 release, but it needs a lot more work to be anywhere near a complete list.

https://github.com/asciidoctor/asciidoctor/wiki/Release-Checklist#stylesheet-qa

We're mostly looking at A/B testing here...so we'd need to establish a baseline, then we can get a report whether the change broke anything unexpected. I'm thinking CasperJS is the solution here (see http://casperjs.org/)