Series of videos are typically uploaded to YouTube playlists in
chronological order. By default, these videos are downloaded
latest-to-earliest; this is great for seeing the latest videos in a
series, but prevents streaming video in the order that the videos were
produced. Add an option to download videos in reverse order,
earliest-to-latest.
Conflicts:
youtube_dl/YoutubeDL.py
youtube_dl/__init__.py
ff815fe65a