Adding Install shell completions automatically

[freexploit]

• Adding a --install flag to the Aiken completion command. When you set this flag to true, Aiken will write to a file instead of just showing you the output.
• Zsh support on linux (basic no plugins like oh-my-zsh yet)
• Fish support on linux
• Bash support on linux
• Tweaking aikup so it automatically runs aiken completion $SHELL --install every time you install a new version.

[KtorZ]

Looks good overall, but I kindly request a few additions on the error context. As much as possible, we should strive for errors to be helpful and provide all the context necessary to troubleshoot problems 👍

[KtorZ]

Thanks ❤️