Major Bug Fix and autoshoot.

I don't know where my mind was when I wrote this game. While preparing the Android version I noticed that the movement and shooting of the player's ship was "straight" (without taking the time elapsed since the last frame into consideration). That's ... quite brain dead on my part.
Anyway, that's fixed, so everybody should have an equally hard time to win.

On the other hand I also added an autofire modus. If you keep space pressed the ship will keep on shooting.

Enjoy.