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/ClientCommandPacket.h

@@ -19,6 +19,6 @@ public:
 	int getEstimatedSize();
 
 public:
-	static shared_ptr<Packet> create() { return shared_ptr<Packet>(new ClientCommandPacket()); }
+	static std::shared_ptr<Packet> create() { return std::shared_ptr<Packet>(new ClientCommandPacket()); }
 	virtual int getId() { return 205; }
 };