Add footers to demos

[oleksiykamenyev]

Hello, could Crispy Doom be updated to write demo files with footers similar to PrBoom+? This would be very useful for the sake of watching demo, and particularly for a smoother maintenance of the DSDA going forward, since it will be possible to determine what IWAD and PWAD the demo used both by manually opening the demo as text and programmatically. Would be really appreciated!

[fabiangreffrath]

I guess this plays along with #8.

[oleksiykamenyev]

Kind of, yeah. I assume this should be much easier, as it's just saving the arguments on the command line to the footer.

I think for the purposes of programmatically determining which wad a demo played back with, this wouldn't need to be cross-compatible with auto-playback in PrBoom+, and I'm not entirely sure whether PrBoom+ would also only play back demos that have the PrBoom source port name in the footer anyway. Just having that info in some readable format would be enough.