A better method for elapsed time

[Libbum]

Take a look at the way image does it

impl fmt::Display for Elapsed {
    fn fmt(&self, out: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match (self.0.as_secs(), self.0.subsec_nanos()) {
            (0, n) if n < 1000 => write!(out, "{} ns", n),
            (0, n) if n < 1000_000 => write!(out, "{} µs", n / 1000),
            (0, n) => write!(out, "{} ms", n / 1000_000),
            (s, n) if s < 10 => write!(out, "{}.{:02} s", s, n / 10_000_000),
            (s, _) => write!(out, "{} s", s),
        }
    }
}