Implement movement and projectiles

[srliao]

Think of a way to implement movement and projectiles.

Movement is for player (and possibly enemy) movement. Projectile is for things such as arrows, catalyst attacks, etc.. Projectiles are important because they have collision detection and depending on the projectile, may kill itself after 1 hit, multiple hits, or time based. They can also have different travel path i.e. straight line (arrows, sort of) vs circular (pyronado)