Make `Key` a clone type

Created by: MovingtoMars

This would be helpful, especially considering Key is a relatively small type.

Created by: ticki

Unfortunately this is not possible due to io::Error's lack of clone.

Created by: MovingtoMars

Have you considered taking the Error variant out of Key, and just iterating over io::Result<Key>?

Created by: ticki

That's a good idea, actually.