Support for top-level/nested `emitKey`/`$`

[andybarron]

For the following JSON:

{
  users: {
    a:  { name: 'User A' }
  },
  posts: {
    b:  { name: 'Post B' }
  },
}

I would love a way to emit the following two outputs:
{ key: ['users', 'a'], value: { name: 'User A' } }
{ key: ['posts', 'b'], value: { name: 'Post B' } }