si-scale 0.1.0

Formats value using the appropriate SI scale. ``` use si_scale::helpers::{seconds, seconds3}; let actual = format!("{}", seconds(1.3e-5)); let expected = "13 µs"; assert_eq!(actual, expected); let actual = format!("{}", seconds3(1.3e-5)); let expected = "13.000 µs"; assert_eq!(actual, expected); ```