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/ChunkPos.h

@@ -13,7 +13,7 @@ public:
 	static int64_t hashCode(int x, int z);
 	int hashCode();
 
-	double distanceToSqr(shared_ptr<Entity> e);
+	double distanceToSqr(std::shared_ptr<Entity> e);
 	double distanceToSqr(double px, double pz);	// 4J added
 
 	int getMiddleBlockX();