Simplify the development code

[emartinez-dev]

I think now it's easier to both reading it and adding more functionalities, but I want you to read the changes to see if you can improve it further or if anything is not clear @Juan-aga. Main changes are:

• The program exits earlier if the scene is badly formed, in previous versions of our program, the MLX window was always displayed and then closed.
• Separate code for object parsing and object representation.
• Sort functions inside files from more abstraction to less abstraction. For example, I have put the functions of the engine in the following order so we can read it from top to bottom:

1. render: there are a lot of thing going on in this function, calls raycast in order to render
2. raycast: calls hit_objects in order to know which object the ray hits
3. hit_objects: calculates object / ray intersection
4. ray_color: calculates the color, lighting and shading of a ray
5. ray_at: utility function to calculate the depth of a ray hit, a very concret thing

• Implement the epsilon variable (smallest value bigger than 0) to compare instead of 0, because when working with doubles, there can be bugs when working with small precision.
• Implement the quadratic equation struct to hold all the necessary variables and a function to calculate the quadratic solution: $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$
• Fix the sphere formula.
• vec3_unit function name is changed to vec3_normalize to better show what it does
• Add more scenes.