Defensor game demo

Miscellaneous Forums/Blitz Showcase/Defensor game demo

I've now updated my Defensor demo to include the following:
- reduced the size of the demo from 2.33 to 1.57 Mb
- improved the particle effects (thanks MasterBeaker)
- increased the shield level from 1 to 10 units, so it's much easier now
- default control option is now keyboard; joystick control can still be selected