Not all done but close

Pausing is in now which is pretty coolies i guess. When paused you can either continue, return to the level select screen or even exit the game completely.

F12 is now the exit at any point key.

So the only critical things left to allow me to make a demo version are:

- a return to main menu button from the level select screen
- level progression to be enabled via...
- end level screen finished including score and other stats

I'd also like to do a couple of tunes for it. Otherwise its comming along fine. I want to get a version out tomorrow but im gonna have to really push it to achieve that.