Macro lambda

macro_rules! lambda {
    ($handler:ident) => { ... };
    ($handler:ident, $runtime:expr) => { ... };
    ($handler:expr) => { ... };
    ($handler:expr, $runtime:expr) => { ... };
}

Starts an event listener which will parse incoming events into the even type requested by handler and will invoke handler on each incoming event. Can optionally be passed a Tokio runtime to build the listener on. If none is provided, it creates its own.