Make Action.Result an ADT
Add Action.Result.NoChange
Add Action.Result.Split
Add Action.Result.Delete
Handle cursor correctly when deleting the last inbox entry
Backfill tests for Outline.Entry.delete
Entries can be deleted
Root entry cannot be deleted
Correctly handle deleting the last item in an array
Correctly handle deleting the last child of an Entry
Extract Entry.do
Backfill tests for Entry.goLeft/goRight
Combine Entry.liftCursorAction with Entry.do
Backfill tests for Entry.insert/backspace
Replace Entry.liftAction with Entry.do, which fixes a bug with backspace