Add M.U.G.E.N. engine.

[MichaelHinrichs]

SteamDB app page links to a few games using this

https://steamdb.info/app/2509830/ https://steamdb.info/app/1431780/

Brief explanation of the change

Find M.U.G.E.N.'s settings and configuration files.

[SteamDB-Tracker]

After running changed rules in this pull request (this bot only tests rules.ini changes):

Changed technologies: Engine.MUGEN

These apps now match: (3) 2016510 2509830 2624830

Please confirm that all these changed apps are correct.

[Lifeismana]

not used by enough apps