code: function writeMessage(channelName, readerUuid, messageJson, paths) {
      paths = paths || getPaths(channelName);
      const time = microSeconds();
      const writeObject = {
          uuid: readerUuid,
          time,
          data: messageJson
      };
  
      const token = randomToken(12);
      const fileName = time + '_' + readerUuid + '_' + token + '.json';
  
      const msgPath = path.join(
          paths.messages,
          fileName
      );
  
      return writeFile(
          msgPath,
          JSON.stringify(writeObject)
      ).then(() => {
          return {
              time,
              uuid: readerUuid,
              token,
              path: msgPath
          };
      });
  }
docs: writes the new message to the file-system
  so other readers can find it
  @return {Promise}