Using https://github.com/asottile/pyupgrade
1. `__future__` imports and `coding: utf-8` were removed
2. Files were rewritten with `pyupgrade --py36-plus --keep-percent-format`
3. f-strings were cherry-picked from `pyupgrade --py36-plus`
Extractors are left untouched (except removing header) to avoid unnecessary merge conflicts
* Add option `--live-from-start` to enable downloading live videos from start
* Add key `is_from_start` in formats to identify formats (of live videos) that downloads from start
* [dash] Create protocol `http_dash_segments_generator` that allows a function to be passed instead of fragments
* [fragment] Allow multiple live dash formats to download simultaneously
* [youtube] Implement fragment re-fetching for the live dash formats
* [youtube] Re-extract dash manifest every 5 hours (manifest expires in 6hrs)
* [postprocessor/ffmpeg] Add `FFmpegFixupDuplicateMoovPP` to fixup duplicated moov atoms
Known issue: Ctrl+C doesn't work on Windows when downloading multiple formats
Closes #1521
Authored by: nao20010128nao, pukkandan
* All modules and binary names are changed
* All documentation references changed
* yt-dlp no longer loads youtube-dlc config files
* All URLs changed to point to organization account
Co-authored-by: Pccode66
Co-authored-by: pukkandan
