[#311] Add maybeAt, !!? with its arguments flipped

[dalpd]

Resolves #311

Hi @chshersh! This wasn't assigned to anyone so I thought I'd give it a go, hope that was OK.

As for the naming: I didn't use one of your suggestions and came up with maybeAt for this but let me know if you all would prefer one of the others in the list. AFAIKT this wouldn't cause any name conflicts so just left it under Relude.List.

Checklist:

HLint

• I've changed the exposed interface (add new reexports, remove reexports, rename reexported things, etc.).
  • I've updated hlint.dhall accordingly to my changes (add new rules for the new imports, remove old ones, when they are outdated, etc.).
  • I've generated the new .hlint.yaml file (see this instructions).

General

• I've updated the CHANGELOG with the short description of my latest changes.
• All new and existing tests pass.
• I keep the code style used in the files I've changed (see style-guide for more details).
• I've used the stylish-haskell file.
• My change requires the documentation updates.
  • I've updated the documentation accordingly.
• I've added the [ci skip] text to the docs-only related commit's name.

[chshersh]

@dalpd Thanks for the contribution! And docs are nice 👍🏻
I left one comment regarding the failing tests.

I think the maybeAt name is fine. It doesn't have conflicts with other functions on Hackage ✔️