partially ported the software to use SDL2
added dumps for debugging
finally ported the project to SDL2. however, we cannot use textures.

textures are kept in video memory and their width/height are limited by the
system. images larger than the native width/height are just truncated.
therefore, we keep using surfaces lying inside the system memory. this puts a
slight overhead for blitting (and converting) the surfaces to the display
surface.