add (Log4r::Logger)

    # File log4r/logger.rb, line 114
        def add(*_outputters)
          for thing in _outputters
            o = (thing.kind_of?(Outputter) ? thing : Outputter[thing])
            # some basic validation
            if not o.kind_of?(Outputter)
              raise TypeError, "Expected kind of Outputter, got #{o.class}", caller
            elsif o.nil?
              raise TypeError, "Couldn't find Outputter '#{thing}'", caller
            end
            @outputters.push o
            Logger.log_internal {"Added outputter '#{o.name}' to '#{@fullname}'"}
          end
          @outputters
        end