Missing reset() method added.

include/unique_resource.h

 #include "scope_exit.h"
 #include <utility>
 #include <type_traits>
+#include <functional>
 
 namespace sr
 {
             return m_value.get();
         }
 
+        void reset(T& newValue) noexcept
+        {
+            m_value = std::ref(newValue);
+        }
+
 
     private: