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
Closes #171
* The structure of the API JSON was changed
* Smile Video seems to be no longer available. So remove the warning
* Move ping to downloader
* Change heartbeat interval to 40sec
* Remove unnecessary API headers
Authored-by: CXwudi, tsukumijima, nao20010128nao, pukkandan
Tested by: tsukumijima
* 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