Could xcb::Event be marked as Send?

[fabriziosestito]

This will allow to use wait_for_event in a future such as:

tokio::spawn(async move {
    loop {
        let event = conn.wait_for_event().unwrap();
        match event {
            xcb::Event::X(event) => {
                sender.send(event).await.unwrap();
            }

            xcb::Event::Unknown(_) => {}
        };
    }
});

[rtbo]

This is actually a bug. Send and Sync is implemented for all event types except UnknownEvent.