Hook up core functions (incomplete)
Hooked up most of the core functions.  Haven't tested extensively yet, and there are still two remaining.  Frame advance and the gameshark button are hard-coded into the core and do not have equivalent functions in the API to use in the front-end.  For frame advance, the M64CMD_SET_FRAME_CALLBACK could be utilized to listen for when one frame has been completed, along with the pause function.  There doesn't appear to be an easy way to access the gameshark without modifying the core.  A hackish solution would be to assign it to a rarely-used SDL scancode, and then inject calls to M64CMD_SEND_SDL_KEYUP and M64CMD_SEND_SDL_KEYDOWN (this could also be used as an easier-to-code implementation for frame advance).  Additionally, I'd like to see a less hackish way to synchronize slot and speed functions between PeripheralController and GameMenuHandler.