code: func (menu *Menu) RadioGroupAtGroupID(groupID uint) []*MenuItem {
  	group := []*MenuItem{}
  	for _, item := range menu.Items {
  		if item.IsGroupID(groupID) {
  			group = append(group, item)
  		}
  	}
  
  	return group
  }
docs: /*
  Find all menu items that belong to group identified by groupID
  Not recursive, as a group should be identified at the same level.
  Since it is not recursive you can theoretically reuse a groupID but problems
  could creep up elsewhere, so please use unique groupID for radio items
  */