log: use forwarding references for format parameters

log.hpp

@@ -82,9 +82,16 @@ namespace util {
 
     template <typename ...Args, size_t N>
     void
-    log (level_t l, const char (&fmt)[N], const Args&...args)
+    log (level_t l, const char (&fmt)[N], Args &&...args)
     {
-        log (l, to_string (format::printf (fmt) (args...)));
+        log (
+            l,
+            to_string (
+                format::printf (fmt) (
+                    std::forward<Args> (args)...
+                )
+            )
+        );
     }