Expose "objectify" as "link".
Add "@embed": "@link" feature and jsonld.link API.

- The `@link` flag can be used along with jsonld framing now in
  order to create in-memory links when embedding nodes in the
  framed output. This feature replaces the old "objectify"
  API (now deprecated). To get a similar result as the old
  "objectify" API call jsonld.link or use a wildcard frame with
  "@embed": "@link" set or set options.embed to '@link'.
Release 0.3.11.
Start 0.3.12.