support Debug trait for diff

[ayourtch]

It could be very handy to display the diff for debugging, but the corresponding trait is not there. I did not study the question in depth so not sure if there is a deep reason for not implementing it, or it is it just a matter of some work ? if the latter - would you be open to a PR implementing that ?

[Jim-Holmstroem]

That would be a very welcomed PR :D
As far as I know there isn't any deep reason for not implementing it, it just haven't been done

Please let me know if you get stuck or have any questions!

Also, I don't have pull rights to this repository anymore, but I'm pretty sure @ramn would be hopeful with that when the time comes