Ported ExPolygon->contour and ExPolygon->holes

xs/xsp/ExPolygon.xsp

@@ -13,6 +13,10 @@
         %code{% RETVAL = THIS->to_SV(); %};
     SV* pp()
         %code{% RETVAL = THIS->to_SV_pureperl(); %};
+    Polygon* contour()
+        %code{% const char* CLASS = "Slic3r::Polygon"; RETVAL = new Polygon(THIS->contour); %};
+    Polygons holes()
+        %code{% RETVAL = THIS->holes; %};
     void scale(double factor);
     void translate(double x, double y);
     double area();