Feature Request - Prune for backup / copy mode

One missing killer feature for backup / copy mode is a prune command.

Input:

• mackup backup prune or w/e makes sense

Output:

• Diff the storage dir against the source & remove any files from the storage dir that no longer exist in the source

This app has made config file redundancy a breeze - prune would be a cherry on top.

Thanks for your effort & considering this feature.