inbucket cmd: add version flag (#385)

cmd/inbucket/main.go

@@ -49,6 +49,7 @@ func init() {
 func main() {
 	// Command line flags.
 	help := flag.Bool("help", false, "Displays help on flags and env variables.")
+	versionflag := flag.Bool("version", false, "Displays version.")
 	pidfile := flag.String("pidfile", "", "Write our PID into the specified file.")
 	logfile := flag.String("logfile", "stderr", "Write out log into the specified file.")
 	logjson := flag.Bool("logjson", false, "Logs are written in JSON format.")
@@ -64,6 +65,10 @@ func main() {
 		config.Usage()
 		return
 	}
+	if *versionflag {
+		fmt.Fprintln(os.Stdout, version)
+		return
+	}
 
 	// Process configuration.
 	config.Version = version