Undo/Redo

[lucthev]

Technically, this should actually be relatively straightforward: listen to the various delta events (/(paragraph|section)(Insert|Update|Delete)/), figure out the opposite of that delta, and pop both, along with a copy of the selection at the time, onto a stack of some kind. Undo/redo is then simply a matter of applying the right deltas.

Trickier, however, is determining when to save the current state. MS Word is nonsensical in when it decides to save state; Sublime Text and Medium seems to base it on word boundaries, which is a much better experience.