production release v2021a_12 coming over the weekend

[Jeremy Faden]

I've made a few more changes to the development release which will
become the production release.  This includes a couple more bugfixes,
like allowing bookmarks to come via GitHub FileSystems, where before
they would have to come from the "raw" version of the site.  PDS4 now
looks for the upcoming lblx extension, and special constants for missing
data values are checked for now.

If you happened to hear about the Log4J Java vulnerability
(https://blog.cloudflare.com/inside-the-log4j2-vulnerability-cve-2021-44228/),
it is a big deal and fortunately it looks like Autoplot is not
affected.  (Minecraft is though, so if your kids have it on the computer
you'll want to update it!)

This is the devel release at https://autoplot.org/jnlp/20211210a/.

Jeremy