Bump HTTP timeout to 5 minutes.

This was done as a result of the pull-request in #30, which
wanted to add user-configurable setting.  I'm aware that there
are a few too many flags in use already, so I'd rather make
the defaults reasonable.

This closes #30.

cmd_serve.go

@@ -1042,8 +1042,8 @@ func serve(settings serveCmd) {
 	srv := &http.Server{
 		Addr:         bind,
 		Handler:      loggedRouter,
-		ReadTimeout:  5 * time.Second,
-		WriteTimeout: 10 * time.Second,
+		ReadTimeout:  300 * time.Second,
+		WriteTimeout: 300 * time.Second,
 	}
 
 	//