Updated Bullet Shooting, please read below

Update regarding bullet shooting:
- Bullet will disappear once it collides with other bullets / aliens.
- BulletCollection still DOES NOT HAVE reload implementation yet, so
please DONT uncomment the fire function on SpaceShip. Otherwise it will
crash.

Details about Games.c:
- I added animation image for bullet (which is star and it's only 1
pixel)
- I modified the constructor of BulletCollection to contain collision
checker

Reason why I commited this commit:
- I need to commit since it is a lot of change already, and by doing
this, whenever there is a new commit I don't have to do all changes.
(hope that make sense :D)