Mario: proper position when standing on ground

mario/mario_visitor.hpp

@@ -38,9 +38,13 @@ public:
     bool canGoRight() {
         return !right;
     }
+    double getGroundY() {
+        return groundY;
+    }
 
 private:
     bool onGround = false;
+    double groundY = 0;
     bool death = false;
     bool stop = false;
     double newX;