Add polygon testing

[AlterEgoIV]

Add (polygon, x), (x, polygon) overlaps, contains, intersects, closest and reflect function stubs
Add (polygon, point) contains function
Add (polygon, polygon) overlaps function
Add (polygon, point) overlaps function
Add Polygon type to ShapeWrap variant
Add draw_internal function for Polygon type
Add regular convex Polygons to ShapeWrap vector

[OneLoneCoder]

Thanks Alter! Before fully jumping on the second and largest polygon implementation PR, I've added a discussion page so we can flesh out the details of this fundamental type, and understand the implications of choosing the structure of such a fundamental, well, structure. Please see #59 and #46