Register a namespace handler object.

        :param namespace_handler: An instance of a :class:`Namespace`
                                  subclass that handles all the event traffic
                                  for a namespace.

def register_namespace(self, namespace_handler):
        """Register a namespace handler object.

        :param namespace_handler: An instance of a :class:`Namespace`
                                  subclass that handles all the event traffic
                                  for a namespace.
        """
        if not isinstance(namespace_handler, namespace.Namespace):
            raise ValueError('Not a namespace instance')
        if self.is_asyncio_based() != namespace_handler.is_asyncio_based():
            raise ValueError('Not a valid namespace class for this server')
        namespace_handler._set_server(self)
        self.namespace_handlers[namespace_handler.namespace] = \
            namespace_handler