[feature] Implement a simplistic model of diffusion

Implement a directional diffusion model with linear attenuation depending on the angle with the lenticular sheet diffuser's normal.
The more the diffused ray deviates from the plane normal, the more it is attenuated.
The rays outside of the viewing angle are suppressed.
Comes with working visualisation (I copied and adapted the "show_light_map" function from light.py to implement it quickly).
This is still Work In Progress, next step is to extend the method to accept n rays as input (for now it only works with 1 ray ; very inefficient).