Atomic: Add operators += and -=

luna/include/luna/Atomic.h

@@ -103,6 +103,16 @@ template <typename T> class Atomic
         return fetch_sub(1);
     }
 
+    T operator+=(const T& other)
+    {
+        return fetch_add(other) + other;
+    }
+
+    T operator-=(const T& other)
+    {
+        return fetch_sub(other) - other;
+    }
+
   private:
     T m_value;
 };