def tag_list=(tags)
      case tags
      when String
        self.tag_names = tags.split(/,\s*/)
      when Array
        self.tag_names = tags
      end
    end
def tag_list=(tags)
      case tags
      when String
        self.tag_names = tags.split(/,\s*/)
      when Array
        self.tag_names = tags
      end
    end
Set a list of tags
 Pass a String with comma separated tag names or
 an Array of tag names