Add missing support for `FORGIT_GLO_FORMAT`

[wallace11]

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

FORGIT_GLO_FORMAT appears in the documentation, but it was not anywhere to be found on the code itself. This PR just adds this missing feature.

Now, before anyone mentions FORGIT_LOG_FORMAT - this global variable needs to be set before forgit is first loaded and cannot be changed during an active session. For me it means to put it in ~/.zshenv which gets loaded before anything else, and I consider this to be less than ideal.

Type of change

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

Test environment

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

[wfxr]

@wallace11 Sorry for the late reply. Looks good to me. Thank you!