Tidy up completions

[chopfitzroy]

Complete

• https://github.com/sharkdp/fd
• https://github.com/ogham/exa
• https://github.com/asdf-vm/asdf

Hoping these can be done with sheldon

Pending #154;

• https://github.com/RichiH/vcsh
• https://github.com/sharkdp/bat
• https://github.com/rossmacarthur/sheldon (potentially open an issue for this one)