Change the way refs get resolved.  Previously we would resolve a ref like:

  'property' => {'ref' => '/some/uri'}

to:

  {
    'property' => {'ref' => '/some/uri'}
    'resolved' => {'property' => {resolved version}}
  }

but now we inline it into the ref itself like this:

  {
    'property' => {'ref' => '/some/uri', '_resolved' => {resolved version}}
  }

This has the nice effect of keeping everything together, so you can access the
resolved version at the same path as the ref itself.