Function game_loop 

pub fn game_loop<G, U, R>(
    game: G,
    updates_per_second: u32,
    max_frame_time: f64,
    update: U,
    render: R,
) -> GameLoop<G, Time, ()>
where
    U: FnMut(&mut GameLoop<G, Time, ()>),
    R: FnMut(&mut GameLoop<G, Time, ()>),