code: function () {
          var prefix = 'DEBUG';
          this.output(prefix, prefix.blue, Array.prototype.slice.call(arguments));
      }
docs: @name debug
  @memberof logger
  @method
  @param {Arguments} messages　Variable argument message
  @example
  logger.debug('hoge', 'foo', 'bar', 10);
  
  > hoge foo bar 10