Merge pull request #404 from dhchen/Log_string

Concatenate log into one string and sending to std::cerr instead of multiple << operator

include/crow/logging.h

@@ -60,7 +60,7 @@ namespace crow
                     prefix = "CRITICAL";
                     break;
             }
-            std::cerr << "(" << timestamp() << ") [" << prefix << "] " << message << std::endl;
+            std::cerr << std::string("(") + timestamp() + std::string(") [") + prefix + std::string("] ") + message << std::endl;
         }
 
     private: