add browser testing via zuul

You can run the tests locally in a browser with:

```
zuul --local -- test/index.js
```

Or you can run the suite in sauce browsers with
```
zuul -- test/index.js
```

I have not hooked up any of the travis stuff, but everything you need is documented here:
https://github.com/defunctzombie/zuul/wiki/Quickstart

Note that some tests are failing in Chrome 31 on windows with xdomain stuff. We ran into this on the engine.io module and believe it to be a bug in chrome on windows.