Change Polygon2d directory and add it to gd namespace

[victorlevasseur]

I think the Polygon2d class is not at the good place in GDCore.
Maybe we can move it from GDCore/BuiltinExtensions/SpriteExtension to another directory. Which one ?
Then, we can move it into the gd namespace (even if it's used by GDCpp's games ?).

[4ian]

For now, most files uses Polygon by refering to GDCpp/Polygon.h (which is nice, but as the class is named Polygon2d, it should be renamed to GDCpp/Polygon2d.h).
No classes in GDCore/PlatformDefinition are using Polygon so I'm not sure it should not be in this directory..

[victorlevasseur]

You've forgotten to change the include in the GDCpp/Polygon2d.cpp file. ;)
(Don't do anything, I've fixed it in a bugfix pull-request for the tilemap object)

[4ian]

Oops, good catch ;)