code: function iconStyle (files, useIcons) {
    if (!useIcons) return '';
    var className;
    var i;
    var iconName;
    var list = [];
    var rules = {};
    var selector;
    var selectors = {};
    var style = '';
  
    for (i = 0; i < files.length; i++) {
      var file = files[i];
  
      var isDir = '..' == file.name || (file.stat && file.stat.isDirectory());
      var icon = isDir
        ? { className: 'icon-directory', fileName: icons.folder }
        : iconLookup(file.name);
      var iconName = icon.fileName;
  
      selector = '#files .' + icon.className + ' .name';
  
      if (!rules[iconName]) {
        rules[iconName] = 'background-image: url(data:image/png;base64,' + load(iconName) + ');'
        selectors[iconName] = [];
        list.push(iconName);
      }
  
      if (selectors[iconName].indexOf(selector) === -1) {
        selectors[iconName].push(selector);
      }
    }
  
    for (i = 0; i < list.length; i++) {
      iconName = list[i];
      style += selectors[iconName].join(',\n') + ' {\n  ' + rules[iconName] + '\n}\n';
    }
  
    return style;
  }
docs: Load icon images, return css string.