Create GFU for fish

[cjappl]

Check list

• [x] I have performed a self-review of my code
• [x] I have commented my code in hard-to-understand areas
• [x] I have made corresponding changes to the documentation

Description

Type of change

• [ ] Bug fix
• [x] New feature
• [ ] Refactor
• [ ] Breaking change
• [ ] Documentation change

Test environment

• Shell
  • [ ] bash
  • [ ] zsh
  • [x] fish
• OS
  • [ ] Linux
  • [x] Mac OS X
  • [ ] Windows
  • [ ] Others:

[cjappl]

Closing #146 for fish.

Thanks to @ArikDavidov for the original work, this is a great feature. Also, it has the funniest name of any of our shortcuts:

"use gfu when you f'd up!"

[cjappl]

@wfxr leaving for you to review. I don't think this ci failure was not on the part of this code change, but I'm unsure how to relaunch

[wfxr]

@cjappl Looks good to me! Thanks for your work!