Steering/Movement Reimplementation

[lunacys]

Closes #15.

This PR splits SteeringHost into 3 different components:

• Position - holds entity's position.
• SteeringHost - holds steering data (current velocity, steering and desired velocity).
• PhysicsParams - holds parameters for SteeringHost (max velocity, max force, mass and friction).

Steering Behaviors are now in a separate module behaviors and are now simple structs which can be held in components (player, enemies, etc).

Implemented behaviors:

• Seek/Flee - move to/from the target
• Pursuit/Evade - move to/from the estimated new position of the target
• Arrival - move to the target, gradually slowing down the closer to the target
• Wander - move around randomly choosing directions
• Collision Avoidance - try to avoid collision with other entities
• Separation - try to stay apart from each other
• Queue - try to not to touch other entities by creating an imaginary queue
• Leader Following - follow chosen leader
• Path Following - follow a path using one of 3 modes: one-way, patrol and looped (circular)

[lunacys]

There might be a better way to handle steering behaviors, but this is the way I came up with.