Macro gbench::log

macro_rules! log {
    ($($arg:tt)*) => { ... };
}

A macro for logging an event.

let a = 0;
log!("A: {}", a);

will write this to the benchmarking file

{
  "cat": "log",
  "name": "A: 0",
  "ph": "I",
  "pid": 0,
  "tid": 0,
  "ts": /* current timestamp */
}