Added crosshairs!

close #16
Fixed camera tracking movement so that when the window is resized, the camera rotation still works. Also fixed the crosshairs a little from having "sharp" edges in its halo.
Emergency commit; Irrlicht now refuses to start.
Fixed segfault issue; I really have no idea why it did that. A `make clean` seemed to do the trick. Also got main character to exist as a Bullet entity.
Overhauled player control. Players are now Bullet rigidbodies that move around via forces applied to them. They collide with others and cannot walk through walls. Movement is also much smoother now that the player is "forced" around.

close #40 #42
Added detection of the players traveling to the opposite side of their court. Eventually this will be changed into a state for the player and the dodgeball server will deduct points from the team accordingly.

close #11