feat(examples): added `mocha-should-wd-appium` example.

Hello,

I added a new example to run `Yadda` tests on mobile devices / simulators. It's using:

* Appium (http://appium.io/)
* Wd (https://github.com/admc/wd)
* Mocha (http://visionmedia.github.io/mocha/)
* Should (https://github.com/visionmedia/should.js/)

It will run the same tests as `mocha-webdriver` example ;)