If my cursor is on a bullet list, and I press Enter to create a new element,
it registers as 5-7 actions in an undo stack, mostly margins adjustments. So to
rewind it, user has to press `Ctrl+Z` 5+ times, which is quite frustrating.
Instead this patch suggests to treat _any_ change that is a result of a single
key press as a single event, so user has to press `Ctrl+Z` just once to undo it