Fix module renames in ext __init__

Author: a-hurst

sdl2/ext/__init__.py

@@ -14,8 +14,8 @@
 from .common import *
 from .draw import *
 from .bitmapfont import *
-from .font import *
-from .gui import *
+from .ttf import *
+from .uisystem import *
 from .msgbox import *
 from .image import *
 from .pixelaccess import *