align Exoskeleton with Backbone#3003 changes

This brings Exoskeleton up to date with https://github.com/jashkenas/backbone/pull/3003.

Instead of the `useNative` flag, simply extend from a view that uses native methods (like [Backbone.NativeView](https://github.com/akre54/Backbone.NativeView)). Instead of a `keepOld` flag to `delegateEvents`, simply delegate more with a direct call to `view.delegate`.