Ability to change cursor image
Pretty much the title.

It used to be possible by editing `pyxel.constants.MOUSE_CURSOR_DATA`, but that's no longer possible:
https://github.com/kitao/pyxel/commit/633a8185d16122a37dca371cff93c7eef874b8e7#diff-c63ca80a88391b3bd30b8f153bdca69907aa28eb7c8df8ffef54b5e639d6ed42L56-L65