Macro make_builtin 

macro_rules! make_builtin {
    ($name:expr, $func_name:ident) => { ... };
    ($name:expr, $func_name:ident, $builtin:ident) => { ... };
    ($name:expr, $func_name:ident, $builtin:ident, $usage:expr) => { ... };
}

Create a static [Builtin] object for registry in bash.