Fix packaging bugs (#129)

Fix packaging bugs (#129)

* Autogenerate `AUTHORS`
* Fix `setup.py` using wrong completion files
* Complete `ChangeLog` -> `Changelog.md` rename
* Make `make tar` respect DESTDIR
* Remove `bin/` `yt-dlp` and `docs/` from tar and sdist
* Make `pypi-files` build all files needed for `python setup.py`
* Add `completions` alias
* Add `devscripts/` and `supportedsites.md` to pip sdist
* Remove `man` target
* Remove `README.txt` from sdist
* Make `clean` more granular
* Move aliases to top

Authored by: hseg <redacted>