Implement .rev() for LendingIterator

[fritzrehde]

I currently have a use-case where I would like to iterate over mutable windows in reverse. Would it be possible to implement .rev() for LendingIterator?
In case you say e.g. a Vec already provides reverse, I would argue those are different use-cases, since reverse reverses the vector in-place, whereas .rev() just iterates from the back.
Thanks for the awesome crate!