code: function withLineNumbers(text, offset, offendingLine) {
      if (typeof offendingLine !== 'number') {
        offendingLine = NaN;
      }
  
      var lines = text;
      if (typeof lines === 'string') {
        lines = lines.split('\n');
      }
  
      return lines.map(function(line, i) {
        line = (i + offset) + ': ' + line;
        if (i === (offendingLine - 1)) {
          line = '\x1B[31m' + line + '\x1B[39m';
        } else {
          line = '\x1B[90m' + line + '\x1B[39m';
        }
        return line;
      }).join('\n');
    }
docs: Prepends each line in a block of text w/ line numbers, optionally
  highlighting a specific line.