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/CaveSpider.h

@@ -13,6 +13,6 @@ class CaveSpider : public Spider
 
 		virtual int getMaxHealth();
 		virtual float getModelScale();
-		virtual bool doHurtTarget(shared_ptr<Entity> target);
+		virtual bool doHurtTarget(std::shared_ptr<Entity> target);
 		void finalizeMobSpawn();
 };