Support access to perlin noise internal data

libs/pcg/include/psemek/pcg/perlin.hpp

@@ -30,6 +30,9 @@ namespace psemek::pcg
 		// y \in [0.0 .. 1.0]
 		float operator()(float x, float y) const;
 
+		auto & grad() { return grad_map_; }
+		auto const & grad() const { return grad_map_; }
+
 	private:
 		gfx::basic_pixmap<geom::vector<float, 2>> grad_map_;
 	};