Macro rpc_call_request 

macro_rules! rpc_call_request {
    ($method:expr, $params:expr, $id:expr) => { ... };
    ($method:expr, $id:expr) => { ... };
}

Create a simple JSON-RPC client call

Usage:

let request = rpc_call_request!("method_name", [1, 2, 3], 42);
let request = rpc_call_request!("ping", 1); // no params