Fix C++ code smells

* Move "using namespace std;" from header to module file (to no longer pollute the global namespace).
* Fix inconsistency of having namespace prefix in test code.
* Add include guard to GildedRose.h.
* Avoid std::endl.
* Have consistent white-space.

cpp/src/GildedRose.cc

@@ -1,5 +1,7 @@
 #include "GildedRose.h"
 
+using namespace std;
+
 GildedRose::GildedRose(vector<Item> & items) : items(items)
 {}
     

cpp/src/GildedRose.h

@@ -1,24 +1,23 @@
+#pragma once
+
 #include <string>
 #include <vector>
 
-using namespace std;
-
 class Item
 {
 public:
-    string name;
+    std::string name;
     int sellIn;
     int quality;
-    Item(string name, int sellIn, int quality) : name(name), sellIn(sellIn), quality(quality) 
+    Item(std::string name, int sellIn, int quality) : name(name), sellIn(sellIn), quality(quality) 
     {}
 };
 
 class GildedRose
 {
 public:
-    vector<Item> & items;
-    GildedRose(vector<Item> & items);
+    std::vector<Item> & items;
+    GildedRose(std::vector<Item> & items);
     
     void updateQuality();
 };
-