Reference relations by 'name' attribute instead of Schema

Schemas are cool, but I don't think we're there just yet. For now, use
a 'name' attribute, which nicely matches the 'name' attribute given in
<link rel="resource"> elements.

This introduces a BC break; each value in Links must now be another
object - an object containing 'href' and 'name' keys rather than a
single string:

`$links: { self: 'http://api/widgets' }` becomes `$links: { self: {
href: 'http://api/widgets', name: 'Widgets' } }`