shared_ptr -> std::shared_ptr

This is one of the first commits in a plan to remove all `using namespace std;` lines in the entire codebase as it is considered anti-pattern today.

Minecraft.World/CarrotOnAStickItem.h

@@ -9,5 +9,5 @@ public:
 
 	bool isHandEquipped();
 	bool isMirroredArt();
-	shared_ptr<ItemInstance> use(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Player> player);
+	std::shared_ptr<ItemInstance> use(std::shared_ptr<ItemInstance> itemInstance, Level *level, std::shared_ptr<Player> player);
 };