"Article" represents a page or a post which consists of web-sites.
"List" represents a post-list which consists of web-sites.
"UrlJoin" generate a relative location from fragments of a URL.
An instance of "List" should have a method "Content".
An instance of "List" needs not have a list of "Article" instances.
"UrlJoin" requires variable-length arguments. Each of them is typed as string.
Convert values typed as int to string to generate the location from them.
Rename "_list.go" to "content_list.go" to build.