Add test cases

Not that I only tested these in Chrome and Firefox. Fake centering is broken in both as captured in #62

Since I tried to develop my own version of this plugin at one point, I have a bunch of test cases lying around that I thought you might be able to use. I've
tested them in firefox and chrome and they work with your plugin the
same as they did with mine. However, I did not test with any IE versions
and, as I recall, there were some issues there with mine so I would
check with this plugin.