Macro flow_begin

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

Convenience macro for the flow_begin function.

Example:

let flow_id = 1234;
flow_begin!(c"foo", c"bar", flow_id, "x" => 5, "y" => "boo");

const FOO: &'static CStr = c"foo";
const BAR: &'static CStr = c"bar";
flow_begin!(c"foo", c"bar", flow_id);