Function unit_str 

pub fn unit_str(val: u64, base: NumSys) -> String

Converts bytes into human readable output.

use rust_apt::new_cache;
use rust_apt::util::{unit_str, NumSys};
let cache = new_cache!().unwrap();
let pkg = cache.get("apt").unwrap();
let version = pkg.candidate().unwrap();

println!("{}", unit_str(version.size(), NumSys::Decimal));