Add file download information window + SHA-256 + more checksums

I'm not the biggest fan of how the info window works, but it works
anyway, and it's easy to apply to *all* the download links.

Also decided to sign & checksum static binaries. Those are just as
important (if not more so) than the source tarballs.

Yes, I did verify that my copies of all the files were still in line
with the other checksums before creating the SHA256 checksums. :)

And I think I'm done fiddling with the site now; This is the last of my
planned changes. ...except that the site kinda sucks in text-mode
browsers now. Hmm. But how do I improve that?

pub/download/nginx-confgen-linux-amd64-1.2.tar.gz.asc

@@ -0,0 +1,16 @@
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