Macro subscribe

macro_rules! subscribe {
    ($message_bus:expr, $actor_ref:expr) => { ... };
    ($message_bus:expr, $actor_name:expr, $actor_ref:expr) => { ... };
    ($bus_name:expr, $message_bus:expr, $actor_ref:expr) => { ... };
    ($bus_name:expr, $message_bus:expr, $actor_name:expr, $actor_ref:expr) => { ... };
}