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/ExperienceItem.h

@@ -9,7 +9,7 @@ class ExperienceItem : public Item
 public:
 	ExperienceItem(int id);
 
-	virtual bool isFoil(shared_ptr<ItemInstance> itemInstance);
-	virtual shared_ptr<ItemInstance> use(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Player> player);
-	virtual bool TestUse(Level *level, shared_ptr<Player> player);
+	virtual bool isFoil(std::shared_ptr<ItemInstance> itemInstance);
+	virtual std::shared_ptr<ItemInstance> use(std::shared_ptr<ItemInstance> itemInstance, Level *level, std::shared_ptr<Player> player);
+	virtual bool TestUse(Level *level, std::shared_ptr<Player> player);
 };