core::writeln!

macro_rules! writeln {
    ($dst:expr, $fmt:expr) => (
        write!($dst, concat!($fmt, "\n"))
    );
    ($dst:expr, $fmt:expr, $($arg:tt)*) => (
        write!($dst, concat!($fmt, "\n"), $($arg)*)
    );
}

Equivalent to the write! macro, except that a newline is appended after the message is written.