* work correctly on other resolutions
   * the puzzle pieces in the texture maps need some transparent
     space around them, so we can use GL_LINEAR interpolation.
     right now, i have to use GL_NEAREST for the puzzle pieces,
     or else i get artifacts when the interpolation picks up
     pixels because of rounding errors
   * the above has been done, but the texture maps include this transparent
     space now, and it shouldn't. some rewrite of the render stuff will be
     required. (when the .map is created, it should take into consideration
     the images with an extra border,  and adjust x y w h accordingly)

 * change snap puzzle piece center to cursor behaviour
   * make this optional?
   * make it smooth?

 * niecer distribution of the preview images on the preview screen
 
 * general code refactoring