code: public JSON with(JSONWriter w)
      {
          if (w == _writer) {
              return this;
          }
          return _with( _features, _streamFactory, _treeCodec,
                  _reader, w, _prettyPrinter);
      }
docs: Mutant factory for constructing an instance with specified {@link JSONWriter},
  and returning new instance (or, if there would be no change, this instance).