Consider adding warnings for unused option items

[upsuper]

It is easy to find that you need to whitelist, blacklist, opaque, etc. something but you forget to, but it is much harder to catch when you forget to remove something from the list.

I think it would be helpful to display some warning information when an item doesn't match anything, so that users are aware that they can remove them.

This may need support from regex crate, I guess. On the API side, I think we can add a new function to Bindings to get that information.

[pvdrz]

Fixed via #1469