Polygon

[lorenzoliuzzo]

In this PR we aim to create a Polygon ShapeKind.
To check for any intersection between a Ray and the polygon we divide it in triangles and check the hit with them.

Thing to do:

• Find the correct way to pass the vertices of each polygon.
• Find how to safely and efficiently store the triangles.
• Find how to avoid cycling over a polygon triangles, maybe using a little BVHTree (if convenient).
• Update examples of Cornell box with Polygons as squared walls.