Macro flow_step 

macro_rules! flow_step {
    ($category:expr, $name:expr, $flow_id:expr $(, $key:expr => $val:expr)*) => { ... };
}

Convenience macro for the flow_step function.

Flow events must be enclosed in a duration event.

Example:

let flow_id = 1234;
{
    duration!("foo", "step_2");
    flow_step!("foo", "bar", flow_id, "x" => 5, "y" => "boo");
}

const FOO: &'static str = "foo";
const BAR: &'static str = "bar";
let flow_id = 1234;
{
    duration!("foo", "step_2");
    flow_step!("foo", "bar", flow_id);
}