Bind collection to model's class.

        If collection was not specialized in process of model's declaration,
        subclass of collection will be created.

def bind_collection_to_model_cls(cls):
        """Bind collection to model's class.

        If collection was not specialized in process of model's declaration,
        subclass of collection will be created.
        """
        cls.Collection = type('{0}.Collection'.format(cls.__name__),
                              (cls.Collection,),
                              {'value_type': cls})
        cls.Collection.__module__ = cls.__module__