720p @ 1000KB/s looks way better than 1080p @ 500KB/s
'' might actually be passed in, so check for None.
Conflicts: youtube_dl/downloader/external.py
Passing source address option to external downloaders
Handling Connection Reset by Peer Error
supported sites link was not opening from README
required a .md at the end.
In preparation for #4822, extend jsinterp by a lot. (We may even have to/want to write a proper interpreter with actual parsing)