Hypermedia controls in responses

[mstade]

We should be able to easily define hypermedia controls, and include these in responses. For instance, a view might link to a css file that defines styles for that view. It's presumptuous of the returned view to assume it's ok for it to inject those styles, but it should be able to link to them such that the client may decide what to do. HTML for instance has the <link> tag which in certain cases (e.g. rel="style") is fetched and processed automatically; a nap client may choose to do something similar.

This ties in with #7 – nap needs a much better API both in terms of representing and producing these messages.