code: function bytediffFormatter(data) {
          var difference = (data.savings > 0) ? ' smaller.' : ' larger.';
          return data.fileName + ' went from '
              + (data.startSize / 1000).toFixed(2) + ' kB to '
              + (data.endSize / 1000).toFixed(2) + ' kB and is '
              + formatPercent(1 - data.percent, 2) + '%' + difference;
      }
docs: Formatter for bytediff to display the size changes after processing
  @param  {Object} data - byte data
  @return {String} Difference in bytes, formatted