Add operator != to Item.

To be able to determine if the last item is visited in main().

src/document.cpp

@@ -38,6 +38,11 @@ using std::istringstream;
 using std::string;
 using std::move;
 
+bool operator !=(const Item &a, const Item &b)
+{
+    return a.guid != b.guid;
+}
+
 Document::Document(Config &cfg)
     : _cfg{cfg}
     , _profile{cfg.data}

src/document.hpp

@@ -42,6 +42,8 @@ struct Item
     string guid;
     string link;
     string title;
+
+    friend bool operator !=(const Item &a, const Item &b);
 };
 
 /*!