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/LevelData.h

@@ -58,7 +58,7 @@ public:
     LevelData(LevelSettings *levelSettings, const wstring& levelName);
     LevelData(LevelData *copy);
     CompoundTag *createTag();
-    CompoundTag *createTag(vector<shared_ptr<Player> > *players);
+    CompoundTag *createTag(vector<std::shared_ptr<Player> > *players);
 
 	enum
 	{