Use returns description as route notes.

I noticed that, for example, the default `/users/login` route's `include` parameter is pretty nonsensical without this data. If the user specifies a returns description, previously it would go nowhere. 

There are two places this could reasonably go. 

In the `notes` field:

![Imgur](https://i.imgur.com/n9lZVGJ.png?1)

Or in the response messages definition:

![Imgur](http://i.imgur.com/sppCvXo.png?1)

Which do you all think is a better place for it? I'm leaning toward response messages, as definitions like `returns: {arg: 'object', description: 'The matching widget from the widget store'}`, which seem reasonable to write, would be out of context in the `notes` field.