Macro relm_state::connect_async_func_full

macro_rules! connect_async_func_full {
    ($class:ident :: $async_function:ident, $relm:expr, $msg:expr) => { ... };
    ($class:ident :: $async_func:ident ( $($args:expr),* ), $relm:expr, $msg:expr) => { ... };
    ($class:ident :: $async_func:ident, $relm:expr, $msg:expr, $fail_msg:expr) => { ... };
    ($class:ident :: $async_func:ident ( $($args:expr),* ), $relm:expr, $msg:expr, $fail_msg:expr) => { ... };
}

Like connect_async_func!, but also return a Cancellable to control the asynchronous request.