rethink class architecture

[lifning]

i think the way the old python-snes classes were laid out is kind of showing its age now that libretro has many more types of "callback" via RETRO_ENVIRONMENT, which would be better-suited for being used by something like OOP inheritance? like have a base emulator class that has null callbacks for everything, and then you subclass it and override the self.video_refresh, self.environ_get_log_interface, etc. methods as needed. currently it's a mess of procedural callback passing, some are lambdas, the environ cb is a big if-else chain that can't be overridden...