parseLinkHeaders doesn't include anchor

[elf-pavlik]

I'm parsing a response conforming to https://solid.github.io/data-interoperability-panel/specification/#agent-registration-discovery

It includes uri, rel, and anchor, parseLinkHeades only gives me the uri and rel

  {
    "rel": "http://www.w3.org/ns/solid/interop#registeredAgent",
    "uri": "https://bob.pod.docker/profile/card#me"
  }

Since HTTP deprecated rev using anchor is often used to use existing predicate in reverse direction in rel