Slight changes to mushrooms and enemies

• Popping mushrooms no longer damage enemies, so players can't use mushroom patches as weapons any more. Mushrooms still damage the player though.
• Now if a blaster sees a player hide, the blaster will keep firing while it runs to the last place it saw the player, before giving up the chase. That makes it hard to kill a blaster by running around a corner and ambushing it, since its shootable bullets are its defense.
• Shooters (the red enemies) would sometimes get wedged in a spot where they couldn't get out. I think I fixed that by letting them see obstructions in a full 360-degree circle, so they'll be able to see that the best way out is sometimes behind them.

Other changes:

• Player ghosts glow now, instead of flickering. Perlin noise FTW.
• I changed the last two levels a little.