System redesign and reorganize.
Replaced switch with if/else in enable/disable callback in ACWorld.
Removed commented includes.
Converted audio handler into a class.
Tidied ACDisplay.
Tidied up graphics and texture loading system.
Made ACWorld variables private.
Changed to local get width height in ACWorld constructor.
Implemented key input callback.
Removed unused function.
Removed callback enable/disable state variables.
Made all variables in ACWorld public.

Needed for making update and draw external to ACWorld.
Plus, making them private just complicates things.
Added app quit function.
Reimplemented audio out stream.
Reimplemented accelerometer.