Add PolygonRegular category to C4Shape category
Update C4Shape+PolygonRegular.m

edits done per Alejandro's suggestion:

-extended variable names to clarify maths
-brackets moved
-needless if changed to else
-incorrect comment of polygon type removed
Update C4Shape+PolygonRegular.h

clarified unclear variable names
committing project file as request (hope this is correct)
Update C4Shape+PolygonRegular.m

-minor formatting changes (moving all brackets to match code style)
-added comments explaining maths
Add new C4Shape category of polygonBySideLength