Day 158: Collision impulses

Today I studied and implemented the code to apply impulses during collisions.
This is done in order to simulate a bounce, not unlike the particle engine. The main difference is the rotation part.

The code is divided in a few main functions:

- A function to calculate the necessary velocity to resolve the contact
- A function to calculate the impulse strength: this was a little harder to understand due to a bad naming convention used in the book that made me misinterpret a variable meaning. In the end it does this: it calculates a unit_delta_velocity, which is the velocity imprinted by an impulse of 1. So the final impulse has a strength of desired_delta_velocity / unit_delta_velocity.
-A function to apply the movement: given the impulse, it is possible to extract the linear and angular velocities pretty easily, and apply them.

This doesn't account for interpenetrarion yet (which I'll hopefully do tomorrow).