Contact list delta-encoding

[jb55]

original idea here: nostr-protocol/nips#349 (comment)

I'm planning on resolving this by creating a delta-contact list format,
so each change can be represented by "diff" of the previous one you have
stored. This will allow us to show every change in a compact way, very
much like "git diff" for your contact list, and it's backwards
compatible with everything. Then you will be able to review and rollback
to any previous revision, perhaps damus can do this automatically if it
sees large drops of contacts at once.

[jb55]

it would be cool to generalize this to any addressable event, where content is diff-encoded. This would allow us to do version control of editable events like longform posts