So, I downloaded all the posts and all their comments from my use Perl blog.
They're in this repo, in the posts/ and comments/ directories, respectively.
They're *more or less* unchanged; I found a couple of HTML infelicities that
made it harder to parse the HTML, so I fixed those manually.

Then I wrote a script that converts all the posts to Markdown. It's the one
called create-new-structure. Since this is a "finite problem", I focused on
making my blog posts come out good, rather than to make a total, long-term
solution. Which means things may or may not work if you try them on your
use Perl blog posts.

I have not released the code in here under any license. If you want to use
it, go ahead. Let me know if it worked. :-)