Macro dyon::dyon_fn

macro_rules! dyon_fn {
    (fn $name:ident () -> $rt:ty $b:block) => { ... };
    (fn $name:ident ($($arg:tt : $t:ty),+) -> $rt:ty $b:block) => { ... };
    (fn $name:ident () $b:block) => { ... };
    (fn $name:ident ($($arg:tt : $t:ty),+) $b:block) => { ... };
}

Used to declare an embedded/external function in Rust which can be called from Dyon.

For example, see "examples/functions.rs".