Update links in docs

- The 'Getting Started' section header no longer exists on that jQuery plugins page so I removed.
- cdn.polyfill.io is now just polyfill.io
- update Apple docs URL to prevent a redirect
- Remove CSS Tricks link to IE-only stylesheets as it only applied to IE9 and below which is no longer supported by H5BP or Microsoft
- Microsoft own docs have a rule to not include the country code so that a user gets the docs in their own locale. so a user in UK would go to https://docs.microsoft.com/en-gb/ and a US user would go to https://docs.microsoft.com/en-us/ etc. I suggest we follow their recommendation here.

dist/404.html

@@ -59,4 +59,4 @@
 </body>
 
 </html>
-<!-- IE needs 512+ bytes: https://blogs.msdn.microsoft.com/ieinternals/2010/08/18/friendly-http-error-pages/ -->
+<!-- IE needs 512+ bytes: https://docs.microsoft.com/archive/blogs/ieinternals/friendly-http-error-pages -->