Dictionary examples incorrect syntax

In README.rdoc the dictionary examples show the `:use_dictionary` and `:dictionary` hash options nested within the `:includes` option. This didn't work for me and after looking through your [tests](https://github.com/mikecmpbll/deep_cloneable/blob/master/test/test_deep_cloneable.rb#L116) I discovered that it's meant to be a top level option.

I've changed the README to this effect and added a line about populating dictionaries automatically -- which I think is a very useful feature! (was for me)