code: public Document<?, ?, WordTag> processDocument(Document in) {
      Document<?, ?, WordTag> d = in.blankDocument();
      d.addAll(process(in));
      return d;
    }
docs: Assigns NER labels to the words in the given Document.
  Implements the {@link DocumentProcessor} interface.  Outputs a new document
  with the same meta-data as the old one, but whose contents are a
  List of {@link WordTag}s, where the tags are the NER labels assigned
  to the word.