* `edit.draw(state, fg, hide_cursor)` -- call this from `on.draw` to display
  the current editor state on the app window as requested in the call to
  `edit.initialize_state` that created `state`. `fg` is the color for
  foreground text (`Text_color` is a good default). Set `hide_cursor` to stop
  showing a blinking cursor (usually because you want a `readonly` editor; see
  below).

* `edit.quit()` -- calling this ensures any final edits are flushed to disk
  before the app exits.