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/BookItem.cpp

@@ -6,7 +6,7 @@ BookItem::BookItem(int id) : Item(id)
 {
 }
 
-bool BookItem::isEnchantable(shared_ptr<ItemInstance> itemInstance)
+bool BookItem::isEnchantable(std::shared_ptr<ItemInstance> itemInstance)
 {
 	return itemInstance->count == 1;
 }