Provide specific support for Chex Quest

* Set window caption to "Chex Quest".
* Automatically load chex.deh if present (but unlike Chocolate DOOM,
don't exit with an error if it isn't there).
* Skip episode menu.
* No crush sound or blood (since corpse is invisible).
* No obituaries.
* No dropped items.
* No additional blood spawned on decorations.
* All blood splats are green.
* Screen flashes green rather than red when injured.