writef: split into writef() and writefv()

src/hulk/serial.d

@@ -40,9 +40,9 @@ struct Serial
      */
     public static void writef(string s, va_list args)
     {
-        hulk.writef.writef(s, args, function void(ubyte ch) {
+        hulk.writef.writefv(function void(ubyte ch) {
                     Serial.write(ch);
-                });
+                }, s, args);
     }
 
     /**