allow padding HumanBytes Display output

[darrell-roberts]

I've updated the Display implementation for HumanBytes so it can accept formatting parameters.

[djc]

So what exactly is this trying to solve? It seems unfortunate that this will need an additional allocation.

[darrell-roberts]

The goal was to be able to output HumanBytes with formatting parameters.

Ex:

#[test]
    fn test_human_bytes() {
        use std::fmt::Write;

        let mut s = String::new();
        write!(&mut s, "{:>10}", HumanBytes(10_000)).unwrap();
        assert_eq!(s, "  9.77 KiB");
    }

I agree though I would not want to incur an additional allocation cost. If there is a better alternative I'd go with that.