Implement `coreutils-ext` package with additional multiplatform programs

[certik]

That way, they could also be installed separately by users of bash/zsh and don't hinder compatibility concerns.

Candidates:

• [ ] open: https://github.com/prefix-dev/shell/issues/109
• [ ] dl (download): https://github.com/prefix-dev/shell/issues/110
• [ ] tar, gz, bz2, unzip: https://github.com/prefix-dev/shell/issues/131
• [ ] ldd: https://github.com/prefix-dev/shell/issues/140
• [ ] kill, ps: https://github.com/prefix-dev/shell/issues/142
• [ ] time: https://github.com/prefix-dev/shell/issues/145
• [ ] printenv: https://github.com/prefix-dev/shell/issues/137

More utilities to consider:

• pushd/popd
• chmod
• chown
• diff
• df
• du
• find
• grep
• xargs
• ping
• more / less
• sleep
• cut

Some other commonly used tools:

• shutdown / reboot
• split
• ssh / ssh-keygen / scp
• vi
• rsync

Full list of the most common commands: https://www.busybox.net/downloads/BusyBox.html

[prsabahrami]

What are the plans regarding this? We can have a separate crate here for this or a new repo..?

[certik]

Maybe we can start here, and later split into a separate repository?

CC @wolfv .