Automatically release updated files periodically

[Doublevil]

As suggested by @fasiha in issue #13, it would be nice to have a workflow (GitHub Actions probably) that automatically builds updated JmdictFurigana files (built with the latest Jmdict and Jmnedict files) and creates a new release every month or so.
This will probably imply changing a few things like upgrading to .net core and having the program download the latest dictionary files instead of reading them from the disk.

I'm going to look into this when I have some spare time.

[Doublevil]

This is now implemented. It should run tomorrow (I set it up to run at 8:00 the 25th of every month).
I'll close this issue if everything goes well with the release tomorrow.

[Doublevil]

And there we go! 😄