## beforeKeyDown callback

The following demo uses `beforeKeyDown` callback to modify some key bindings:

- Pressing DELETE or BACKSPACE on a cell deletes the cell and shifts all cells beneath it in the column up resulting in the cursor (which doesn't move) having the value previously beneath it, now in the current cell.
- Pressing ENTER in a cell (not changing the value) results in pushing all the cells in the column beneath this cell down one row (including current cell) resulting in a blank cell under the cursor (which hasn't moved)