Build a list item from the HTMLOptionElement
@param  {int} i      HTMLOptionElement index
@param  {HTMLOptionElement} option
@param  {bool} group  Has parent optgroup
@return {void}
function(option, data) {
  data = data || option;
  var content = this.customOption ? this.config.renderOption(data) : option.textContent;
  var opt = util.createElement("li", {
    class: "selectr-option",
    html: content,
    role: "treeitem",
    "aria-selected": false
  });

  opt.idx = option.idx;

  this.items.push(opt);

  if (option.defaultSelected) {
    this.defaultSelected.push(option.idx);
  }

  if (option.disabled) {
    opt.disabled = true;
    util.addClass(opt, "disabled");
  }

  return opt;
}