Add support for keyboard shortcuts on multi-selection menus

[tbarusseau]

Currently, running git cm offers a quite lengthy menu:

$ git cm
? Select the type of change that you're committing: ›
❯ feat: A new feature
  test: Adding missing tests or correcting existing tests
  ci: Changes to our CI configuration files and scripts (example scopes: Travis, Circle, GitHub Actions)
  build: Changes that affect the build system or external dependencies (example scopes: cargo, bazel, make)
  style: Changes that do not affect the meaning of the code (white-space, formatting, etc)
  chore: Other changes that don't modify src or test files
  perf: A code change that improves performance
  fix: A bug fix
  revert: Reverts a previous commit
  docs: Documentation only changes
  refactor: A code change that neither fixes a bug nor adds a feature

Being able to instantly select one with a key-press would make it really faster to use.

I'm thinking about some letter hints, which are indicated by a line below the relevant character.

[mainrs]

I like the underline thingy! I was thinking about maybe adding a fuzzy search, where you can type for example fix and it filters out everything that matches it.