support of Google App Engine

[sebastienfr]

To enable the support of Google App Engine insert the following code in your main :

func init() {
   err := InitLog(logLevel, logFormat)
   if err != nil {
       logger.WithField("error", err).Warn("error setting log level, using debug as default")
   }

   logger.Warn("Start")
   n, err := BuildWebServer()
   http.Handle("/", context.ClearHandler(n))    
}

Thanks to @ggarnotel for the report.