* uses WebPack to bundle the library into a single JS file,
  which can be downloaded by web browsers from a CDN
* same-origin policy requires that this library
  can only be called from a page hosted by 'youtube.com',
  which limits the use-cases for this build to mainly:
  - browser extensions
  - userscripts

status:
=======
* the example userscript indicates that the Promise returned from:
    window.ytdl.getInfo(window.location.href)
  catches an Error caused by the server response status code: 410
* the corresponding request looks OK:
    https://www.youtube.com/get_video_info?video_id=...
  but something is clearly breaking;
  a closer look is required.

* the issue was the dependency: 'miniget'
  - it performs a GET request,
    with some configurable behavior
  - it uses several native node modules,
    for which I had previously included polyfill libraries
  - ultimately, it just wasn't working
  - I replaced it with a mock implementation,
    which uses 'window.fetch' to perform the network request

status:
=======
* the example userscript works great

add support for:
  options.requestOptions.headers
  options.requestOptions.proxyUrl
  options.requestOptions.debug

example:
========
  window.ytdl.getInfo(
    'https://www.youtube.com/watch?v=CICY20dQUPk',
    {
      requestOptions: {
        headers: {"x-requested-with": "ytdl-core"},
        proxyUrl: "https://cors-anywhere.herokuapp.com/",
        debug: false
      }
    }
  )

where:
======
  https://cors-anywhere.herokuapp.com/corsdemo

test temporary access to demo proxy server:
===========================================
{
  const proxy  = 'https://cors-anywhere.herokuapp.com/'
  const target = 'http://httpbin.org/get'
  const url    = proxy + target

  fetch(url, {headers: {"x-requested-with": "ytdl-core"}})
  .then(req => req.text()).then(console.log)
}

related:
========
* using with proxyAgent in node
    https://github.com/fent/node-ytdl-core/blob/v4.11.5/example/proxy.js
* using with proxyUrl in browser
    https://www.npmjs.com/package/ytdl-core-browser
    https://www.npmjs.com/package/ytdl-core-info-browser

notes:
======
* 'cors-anywhere' limits 50 requests per hour per URL origin
  - apparently, this count is not per-user
  - as such, the example userscript tests on a low-traffic domain:
      'example.com'
* using a proxyUrl, such as 'cors-anywhere', only works on sites
  having a permissive CSP that allows cross-origin fetch
  to 'www.youtube.com'
  - for example, it won't work on 'github.com'

in addition to the existing es2020 target,
add a new es5 target.. along with examples.