SI, IEC, BS1852 compatible number formatter
$ npm install prefix-si
prefix = require("prefix-si").prefix
// import { prefix } from "prefix-si"
prefix(1024*1024, "B", {binary: true})
// => "1MiB"
prefix(1200, "g")
// => "1.2kg"
prefix(4700, "R", {bs1852: true})
// => "4K7"