README: Drop '32-bit only', mention Pyhton 3 and raise required Python to 2.5+
README: Drop '32-bit only', mention Pyhton 3 and raise required Python to 2.5+

niklaskorz/pyglet,adamlwgriffiths/Pyglet,adamlwgriffiths/Pyglet,adamlwgriffiths/Pyglet,niklaskorz/pyglet,niklaskorz/pyglet,adamlwgriffiths/Pyglet,niklaskorz/pyglet