Fixed a bug that made some boxes' background transparent under certain conditions.
Changed the format of the generated box from png to gif. Even if they are gifs, it's still static images.
The name of the image has also changed from undertale_box.png to undertale_text_box.gif, but any link to the old name will be redirected to the new one.
The error that didn't allow changing modes while using the generator through a third party app has been fixed.