Added in deep compare option for bind and documented bind feature

First off, thanks for making a great localstorage module.  I especially liked that it basically worked with everything, arrays and all, out of the box.

I had a complicated array structure that I wanted to store and as per http://stackoverflow.com/questions/14712089/how-to-deep-watch-an-array-in-angularjs
the advice was to use $watch instead of $watchCollection to deal with the deep comparision that I needed.  

It's a relatively small change and I hope my documentation on bind is helpful to others as well.