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/BookItem.h

@@ -7,6 +7,6 @@ class BookItem : public Item
 public:
 	BookItem(int id);
 
-	bool isEnchantable(shared_ptr<ItemInstance> itemInstance);
+	bool isEnchantable(std::shared_ptr<ItemInstance> itemInstance);
 	int getEnchantmentValue();
 };