projectiles

- [x] create a projectile class to generalize all projectiles
- [x] parameters can include: direction angle, type of projectile, projectile speed
- [x] add so player can shoot on click at the angle from the player to the mouse
- [x] turrets can shoot projectiles
- [ ] zombies can shoot projectiles in the future (?)
- [ ] projectiles should be destroyed when they hit a wall

there can either be:

a single projectile class that can be passed a certain projectile id, and the id just determines what it looks like and how much damage it does
or
a projectile class that handles the basics like the direction and the speed and there can be other classes that extend projectile and that handle their own looks, damage, and other things

ideally all projectiles in the game should behave somewhat the same, the only thing that would vary from projectile to projectile is what they look like, what they deal damage to, how much damage they do, how fast they go, and the direction that they are going