Added support for MultipleAdSizes and 64-bit

The guys from [Skoften.net](http://skoften.net) asked me to implement [MultipleAdSizes](https://developers.google.com/mobile-ads-sdk/docs/dfp/ios/banner#multiple_ad_sizes) on IOS. I made the following changes:

* Implement MultipleAdSizes
* Added support for [64-bit](http://www.appcelerator.com/blog/2014/11/alpha-version-of-titanium-sdk-64-bit-support-now-available/)
* Added adWidth/adHeight as described in documentation/example
* Updated documentation
* Updated example app.js