Macro co

macro_rules! co {
    ($name:expr, $f:expr, $size:expr, $priority:expr $(,)?) => { ... };
    ($f:expr, $size:literal, $priority:literal $(,)?) => { ... };
    ($name:expr, $f:expr, $size:expr $(,)?) => { ... };
    ($f:expr, $size:literal $(,)?) => { ... };
    ($name:expr, $f:expr $(,)?) => { ... };
    ($f:expr $(,)?) => { ... };
}

Create a new coroutine.