Feature: support for undo and redo functionality

[Joshswooft]

I would like to support undo/redo using "ctrl + z" (or any keybind, i think this should be customizable for users along with any existing keybindings we have setup within svelvet but thats another feature in itself).

I know I can possibly hook onto the various events you have exposed to us via the library but I can imagine this feature being quite popular so I would like to propose it to be added to svelvet instead.

Happy to throw ideas around on how this could possibly be implemented :)

[Joshswooft]

I think if you could also expose some kind of action store which contains all the actions made by user(s) then this could setup additional functionality for the users of this library like realtime collaboration!!