checkImage keycodes are invalid

[sb8244]

The key property is loosely checked as 46, 8. I noticed on Chrome that the evt.key property comes back like "Backspace" or "Delete". I adjusted the function to get deletion working in my modified code:

if (
  (evt as KeyboardEvent).key === 'Backspace' ||
  (evt as KeyboardEvent).key === 'Delete'
)

[sb8244]

Also, big thanks for making this library TS compatible and for fixing the window dependencies. It seems to work well for me so far.