refactor node center.

lichao

2021-05-20 101b5cf85397ef9350aaedd12cfcf9fd3d07a565

 src/exported_symbols

@@ -5,6 +5,7 @@
   BHUnregister;
   BHRegisterTopics;
   BHQueryTopicAddress;
   BHQueryProcs;
   BHSubscribeTopics;
   BHStartWorker;
   BHHeartbeatEasy;