Binding the update in the root view

Firstly, thanks so much for your widget, you have done a great job with it!

Being new to Alloy, it took me quite a long time to work out how to use this properly in combination with collection binding. I think this was mostly due to having to define the ListView in it's own separate controller.

With this commit:
https://github.com/cornflakesuperstar/Alloy-PullToRefresh/commit/84779451db734e7133059b1345993198d184a8b2

I have created a sample project that adjusts this behaviour.

Perhaps this example would also make things a bit simpler for others to understand how to use your widget? Here's the implementation:
https://github.com/cornflakesuperstar/Alloy-PullToRefresh-Example

Thanks again!