Properly export all lua-facing functions and use those for initialization (love.cpp no longer explicitly mentions implementations)

src/modules/physics/box2d/wrap_PolygonShape.h

@@ -34,7 +34,7 @@ namespace box2d
 {
 	PolygonShape * luax_checkpolygonshape(lua_State * L, int idx);
 	int w_PolygonShape_getPoints(lua_State * L);
-	int luaopen_polygonshape(lua_State * L);
+	extern "C" int luaopen_polygonshape(lua_State * L);
 
 } // box2d
 } // physics