Added fish shell completions.

[eth-p]

Added some completions for fish shell.

[sharkdp]

Thanks!

There is a way to auto-generate completion files for bash, zsh, fish and PowerShell via clap (see for example: https://github.com/sharkdp/fd/pull/66/files, https://github.com/sharkdp/fd/blob/master/build.rs) which I would prefer in order tp prevent maintenance overhead.

What do you think?

[eth-p]

That's a pretty cool feature! Automatically generating completion files would definitely be the way to go.

[sharkdp]

I hope it's okay if I close this PR. I have opened #115 to track the addition of auto-generated completion files.

Thank you very much for your contribution.

[sboukortt]

Unfortunately, the generated fish completion does not complete filenames, and so pressing Tab does nothing for them. That’s sufficiently annoying that I simply deleted the completion file on my machine.

[sharkdp]

@sboukortt Oh ☹️. Could you please open a new ticket to address this?

[sboukortt]

Done (#372), thanks for the suggestion.