code: public Coref newCoref(List<Span<Term>> mentions) {
  	String newId = idManager.getNextId(AnnotationType.COREF);
  	Coref newCoref = new Coref(newId, mentions);
  	annotationContainer.add(newCoref, Layer.COREFERENCES, AnnotationType.COREF);
  	return newCoref;
      }
docs: Creates a new coreference. It assigns an appropriate ID to it. The Coref is added to the document.
  @param references different mentions (list of targets) to the same entity.
  @return a new coreference.