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/ComplexItem.h

@@ -14,5 +14,5 @@ protected:
 
 public:
 	virtual bool isComplex();
-	virtual shared_ptr<Packet> getUpdatePacket(shared_ptr<ItemInstance> itemInstance, Level *level, shared_ptr<Player> player);
+	virtual std::shared_ptr<Packet> getUpdatePacket(std::shared_ptr<ItemInstance> itemInstance, Level *level, std::shared_ptr<Player> player);
 };