chocolate-doom split

[Alexandre Detiste]

Heretic & Hexen have existed for a longtime, so we are stuck with the
-wad suffix;
we can as well use it for the demo's for consistency.

Strife is a new thing so I would go for -data , like all the other
supported new games.
(e.g. : Hacx , ChexQuest, all other non doom-engine games...)

> Please excuse my stupid questions, but I really fail to understand what
> is going on here. :/

Backward compatibility is the key, like when the chocolate-doom
recommends chocolate-heretic not to break current setup.