Replaying `id1` with the `mg3` mechanics is incredible

Having played through the original campaign on Nightmare _at least_ half-a-dozen times -- as well as nearly all the mods in the Kex list -- I was blown away by how much the original levels spring to life just by limiting the inventory, removing ammo drops & buffing cell crates from 6/12 to 10/20.

I really hope these mechanics become the new standard for future mods, and maybe can be backported to older mods with an option or difficulty setting. Copper is great, but what Machine Games showed is that it doesn't go far enough.

Shortlist of notable improvements:

1. Gibbing is _awesome_ now as there's no stress over lost ammo
1. Likewise, there's no longer any interruption to game flow by fretting over drop pickups
1. The Thunderbolt becomes _way_ more viable for regular use, instead of being relegated to Anti-Shambler Spray
1. This in turn makes the Spawns much easier to deal with, seemingly confirming my personal theory that the Thunderbolt was always intended as their counter

Best moment: Running out of ammo while fighting a Fiend in Ebon Fortress & being forced to beat it to death with the axe. I can't conceive of such a thing even being _possible_ under the id1 mechanics.

Biggest surprise: Sandy's episode goes from (arguably) the hardest to by far the easiest & most ammo-rich of the post-shareware episodes. A big part of this is the Thunderbolt ammo count boost, which makes the episode feel much more like an end-of-game blowout. Nameless City, for instance, is _so much more fun_ now.

Smallest surprise: Romero's sadistic streak really shines, as he gives you _just enough_ ammo crates to get by, _if_ you're highly efficient. I think his episode is the only one where sub-par play can soft-lock progression.

Finest chinstroke: The mg3 mechanics really heighten the brutality of the 'Quake' world, to the extent that one decision I was initially disappointed by -- the lack of Copper-style armor preservation with the Pentagram of Protection -- suddenly became extremely fitting.

Minor request: the one thing I really like from Copper is the Spawn de-aggroing if you go out of its line-of-sight long enough. Somehow that behavior seems to fit the creature very well.