docs: def gen(mimetype):
      """``gen`` is a decorator factory function, you just need to set
      a mimetype before using::
  
          @app.route('/')
          @gen('')
          def index():
              pass
  
      A full demo for creating a image stream is available on
      `GitHub <https://github.com/kxxoling/flask-video-streaming>`__ .
      """
      def streaming(func, *args, **kwargs):
          @wraps(func)
          def _():
              return Response(func(*args, **kwargs),
                              mimetype=mimetype)
          return _
      return streaming