ESModules?

I'd like to use certain functions from the package (mostly just the util functions for validation) in a frontend Next.js app. Since the package is currently being exported using CommonJS, no tree-shaking can occur.

This means anyone who visits the site would download the entire `ytdl-core` package even though only a small fraction of it is being used.

If `ytdl-core` offered ECMAScript modules exports (in addition to CommonJS) bundle sizes can be optimized on the web.