XeO3: Pickups.

I've now added those commands; didn't take long, and now I've moved on to do the pickups. What I now have running is a set of 5 baddies where all of them need to be shot and the last one then explodes and drops a coin (or any pickup at all in fact). I had to add a NOSHOOT flag as well and make it different from NOCOLLISION so that you can't shoot the pickup, but explosions also won't harm you. I guess I could have left NOSHOOT out and just set the number of hits to something insane, but this feels a little cleaner. So now all I need to do is get instructions from Luca on how the weapons and pickups actually work! Then we can finish with this bit and move on. Also means Luca can plan out the levels a bit better with all the bits in the right places. I only have a couple of bits left - I hope I don't need to add too many more flags!