fnaify for FNA-based games

[coypu%sdf.org@localhost]

Hi all,

I've imported openbsd gaming's fnaify and some of the related packages,
done by thfr@ and others in OpenBSD.

This is a wrapper to help run games using FNA, an accurate, open source
rewrite of Microsoft XNA Game Studio 4.0: https://fna-xna.github.io/

With FNA, Mono, and the fnaify wrapper, you should be able to run a
non-trivial number of games, worth trying are items in this README
list: https://github.com/rfht/fnaify
(Note: actual list is shorter for pkgsrc since I didn't import steamworks,
and some games may have had a new version that no longer works with this
wrapper)

I imported the package after testing a single game: Celeste.
https://mattmakesgames.itch.io/celeste
running on NetBSD: https://i.imgur.com/ZBHQGTY.png (caveat: no audio)

You should be able to `make install` in games/fnaify and then, given a
FNA-based game, run `fnaify` in the directory of it.

Enjoy.