Modernize

[jimmywarting]

Hi, i wonder if i can modernize this package a bit.

• Switch to using class + extend
• const / let
• remove some old util function with native functionality
• spread arguments
• Drop support for older browser like IE11
• Drop support for older node versions to LTS (those who support ESM) ^12.20.0 || ^14.13.1 || >=16.0.0
• Switch from commonjs to ESM
• Less use of Buffer where it seems fit and replace it with plain Uint8Array (so maybe we don't have to import Buffer to browser)
• perhaps some other stuff as well