function RedirectTransform(res, options) {
  if (!(this instanceof RedirectTransform)) {
    return new RedirectTransform(res, options);
  }

  stream.Transform.call(this, options);

  this._bufferedChunks      = [];
  this._directive           = '';
  this._directiveByteLength = 0;
  this._finished            = false;
  this._res                 = res;
  this._skipRemainingChunks = false;
}
Transform stream that reads up to the first 1,024 bytes of the incoming stream
and looks for a `!rawgit-redirect` directive.

If it finds one, the given response will be redirected to the URL specified by
the directive. Otherwise the incoming stream will be passed through unmodified.

@param {http.ServerResponse} res
  Express response object.

@param {Object} [options]
  Stream options.