Pytube

* Fixes the issue where the transform_plan wasn't parsing correctly

* Improves the CLI by adding a --list-captions tag, and adding a default download quality instead of silently failing.

* Got rid of incorrect hard-coded fps values in favor of determining from the stream metadata.

* Fixed an issue where Playlist objects could not iterate over videos if the playlist was part of a series.

Fixes type annotation errors with on_progress and on_complete callbacks

* Video metadata can now be subscripted.

All exceptions relating to failure to load a video, such as RecordingUnavailable, VideoPrivate, LivestreamError, etc., now inherit from the base VideoUnavailable exception. This allows users to more easily catch all exceptions where a video is unavailable.

Additionally, more handling has been added to improve our ability to detect unavailable videos.

Improvements:
* More accurate itags
* More precise exceptions for unavailable videos
* More robust parsing of video information
* Reduction in overall number of network calls for longer-running applications

Bugfixes:
* Empty StreamQuery object
* Playlists not loading correctly