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/HouseFeature.cpp

@@ -184,7 +184,7 @@ bool HouseFeature::place(Level *level, Random *random, int x, int y, int z)
         }
     }
 
-    shared_ptr<PigZombie>(pz) = shared_ptr<PigZombie>(new PigZombie(level));
+    std::shared_ptr<PigZombie>(pz) = std::shared_ptr<PigZombie>(new PigZombie(level));
     pz->moveTo(x0 + w / 2.0 + 0.5, y0 + 0.5, z0 + d / 2.0 + 0.5, 0, 0);
     level->addEntity(pz);