More fine-grained undo history

[Thomas Buckley-Houston]

When undoing, vim defaults to 'actions' that don't always correspond to what one would normally consider as a single edit, typing, pasting, etc.

Explore using something like triggering history entries with <Space> as suggested here: https://stackoverflow.com/questions/2895551/how-do-i-get-fine-grained-undo-in-vim/4360415#4360415