Add extra information about request handler and its params

def document(info=None, input=None, output=None):
    """
    Add extra information about request handler and its params
    """
    def wrapper(func):
        if info is not None:
            setattr(func, "_swg_info", info)
        if input is not None:
            setattr(func, "_swg_input", input)
        if output is not None:
            setattr(func, "_swg_output", output)
        return func

    return wrapper