Commented out bullet and tile collisions.

It looks like enemies end up shooting at the edge of an impassable tile
and a heinous chain of bullet sounds ensues. Removing collisions between
bullets and tiles helps performance slightly, and it also helps enemy
bullets actually go somewhere. I also added shooting images for all
characters. If someone could implement that simple sprite image while
heroes and enemies are shooting (as opposed to the rotating arm
conundrum), we could move on with polishing the project.