merging features from backbone-nested into backbone-deep-model

as per issue #14, I've added these features from backbone-nested:
* square array backet syntax
* add() function to append to arrays
* remove() function to remove items 

All unit tests pass. Still to do:
* add valuable unit tests from backbone-nested to verify these new features
* documentation to explain the new features

IMPORTANT: technically we are breaking the API with these changes. If we decide to adopt this, we must roll up the major version number to follow semantic versioning (i.e., 0.10.0 -> 1.0.0)

feedback sorely needed, especially @afeld and @powmedia