Saucelabs badge and full integration

This time I tweaked the existing tests so that they work with Expect.js intead of Chai. The result is that we can run the same tests in Node and browsers.

Things to keep in mind:
  * We shouldn't run browser tests twice in Node 0.10 and Node 0.11. I'm skipping tests in Node 0.11. We should do the same in future versions so that we don't send too many tests to Sauce.
  * Chais `respondsTo` doesn't work in Expect.js.
Let's use the https://shields.io/ badges in the same way we're doing on all the other repos.