chore: (if|when)-let macros obsolete; use -let* counterparts

[ashton314]

Emacs 31 makes if-let and when-let macros obsolete. I'm getting warning messages whenever I boot up Emacs about this. This commit switches if-let → if-let* and when-let → when-let*. The warning goes away with this change.

Also, fixed a typo in CONTRIBUTING.org.

[bdarcus]

Thanks, though the CI is complaining, in one case because we're testing an old version of Emacs! Not sure why the other error ATM.

While were here, is it worth bumping the version number, or minimum required Emacs version?

[roshanshariff]

I can't check right now, but does depending on the compat package help? I would hope it defines those starred macros for older Emacs versions as well.

[bdarcus]

I can't check right now, but does depending on the compat package help? I would hope it defines those starred macros for older Emacs versions as well.

It looks like yes:

https://elpa.gnu.org/packages/doc/compat.html

Can you give that a try @ashton314?

[ashton314]

I'm not familiar with compat, but I'll give it a shot.

[ashton314]

@bdarcus Added compat. I'm not sure what version to use—I'm just following what minad has in his vertico package.

[bdarcus]

Thanks @ashton314 !