/// Returns a human readable String of a Duration
///
/// Example: `3h 12m 53s`
pub fn format_duration(d: &std::time::Duration) -> String {
    let mut s = String::new();
    let mut append_unit = |value, unit| {
        if value > 0 {
            s.push_str(&format!("{}{}", value, unit));
        }
    };

    let seconds = d.as_secs() % 60;
    let minutes = (d.as_secs() / 60) % 60;
    let hours = (d.as_secs() / 60) / 60;

    append_unit(hours, "h ");
    append_unit(minutes, "m ");
    append_unit(seconds, "s ");

    s.trim_end().to_string()
}