Macro cmd

macro_rules! cmd {
    ($(@head ($($head:tt)* ))? $curr:literal $(, $($tail:tt)*)?) => { ... };
    ($(@head ($($head:tt)* ))? $curr:expr $(, $($tail:tt)*)?) => { ... };
    (@head ($($head:tt)* )) => { ... };
    (@last $this:expr, $($arg:expr),* $(,)?) => { ... };
}

easy syntax to create a Command

(A1, A2, A3) expands to

A1.cmd().await?
    .arg(A2)
    .arg(A3)
    .kill_on_drop(true)

If An is a string literal, it is replaced with format!(a)