Usage: rebar metrics [--since <date>] [--until <date>] [--output json|text]   (render the full metric registry over a date range)
       --since <date>   lower bound of the reporting window (ISO-8601)
       --until <date>   upper bound of the reporting window (ISO-8601)
       --output         json (default) emits {since,until,metrics{<id>:...}}; text emits one line per metric in registry order
