bubbles 3.1.1

#[macro_export]
macro_rules! die {
    () => (eprint!("\n"));
    ($fmt:expr) => (eprint!(concat!($fmt, "\n")));
    ($fmt:expr, $($arg:tt)*) => ({
        eprint!(concat!($fmt, "\n"), $($arg)*);
        std::process::exit(-1);
    });
}