Caching + Loading Speedup

You might have noticed that the first time you load some of the included models that there's quite a long hang, while it's almost instant there after.  The reason this happens is because the shader behind the model is being cached by your graphics card.  I'm taking some steps to improve this by refactoring the shaders and making them a lot slimmer to compile.  On my rig caching takes 2-5 seconds depending on the complexity of the model.  Hopefully this makes PxBoy just slightly more usable for folks, this will be included in the next update.