Mario: better mushroom movement

mario/visitors/mushroom_visitor.hpp

@@ -40,10 +40,14 @@ public:
     bool getDeath() {
         return death;
     }
+    double getValidXPos() {
+        return validXPos;
+    }
 
 private:
     bool onGround = false;
     double groundY = 0;
+    double validXPos = 0;
     bool stop = false;
     bool left = false;
     bool right = false;