def stream=(stream)
      logger = Logger.new(stream)
      logger.level = @logger.level
      logger.formatter = @logger.formatter
      @logger = logger
    end
def stream=(stream)
      logger = Logger.new(stream)
      logger.level = @logger.level
      logger.formatter = @logger.formatter
      @logger = logger
    end
Sets the logger to use the stream specified. This method is executed
 asynchronously.
 @param [IO] stream stream to write log messages to