Temporal quantification.

Examples:

There are multiple ways to create a new [Duration]:

# use std::time::Duration;
let five_seconds = Duration::from_secs(5);
assert_eq!(five_seconds, Duration::from_millis(5_000));
assert_eq!(five_seconds, Duration::from_micros(5_000_000));
assert_eq!(five_seconds, Duration::from_nanos(5_000_000_000));

let ten_seconds = Duration::from_secs(10);
let seven_nanos = Duration::from_nanos(7);
let total = ten_seconds + seven_nanos;
assert_eq!(total, Duration::new(10, 7));