Add PolygonRegular category to C4Shape category

Added PolygonRegular category to C4Shape category
next i am thinking to extend this category with an "isStar" boolean value to allow user to easily create star shapes!

something like: (instancetype)polygonRegularWithCenter:(CGPoint)c sideLength:(float)l numberOfSides:(int)n eulerAnglePolyIsRotated:(float)e isStar:(bool)s