2D raycast lighting

[Juyas]

• tangent point calculation
• raycast against polygons
• raycast against circle
• light - color support and gradient
• opacity

[Juyas]

fork/lightrays

[Juyas]

having some talk with @athaun and @PixelRifts about how to implement this the right, we didnt agree yet.
compute shaders and different solutions for dividing up the process were discussed.