There is no such thing as "Sub Posts" in Wordpress already built in.
But it could be possible that you create a plugin that is introducing "Sub Posts" in the style you describe them.
Technically you're not talking about subposts but about the URL-Layout. So in Wordpress you add an endpoint ("changelog") that you can handle with some plugin, for example switching display to some other post.
Once this did not properly work with endpoints but I think it's somehow fixed now. Haven't used it tough, so my answer is only informative so far.
