[Feature Request] Add Heretic, Hexen: Beyond Heretic (and Deathkings), and Strife: Veteran Edition Support

[MasterO2]

@nstlaurent

Given that they are Doom-engine games, they should be supported in the future as well:

https://github.com/OpenSourcedGames/Hexen

https://github.com/OpenSourcedGames/Heretic

https://github.com/svkaiser/strife-ve