one hit comment now shows correct value to use

some guns do less than one damage per shot (vulcan gun does 0.5), so
Instant Death Mode needs to max at 0x0.0001, the smallest nonzero value
in Pico-8's fixed-point numeric type.

One Hit Mode is just a comment for now, but I've been uncommenting it
to test it. Note that replacing the health meter with a "!" is triggered
by max HP + max shield <= 1 because 1 hp shows an empty bar.

this needs some more special cases for low-HP ships with active shields.

vacuum_gambit.p8

@@ -911,9 +911,11 @@ player = ship_m.new{
 mknew(player,
  function(p)
   p.main_gun = zap_gun.new()
-  -- ONE HIT MODE
-  -- p.hp = 1
-  -- p.maxhp = 1
+  -- ONE HIT MODE: max hp is
+  -- minimum nonzero value.
+  --
+  -- p.hp = 0x0.0001
+  -- p.maxhp = 0x0.0001
   -- p.shield = 0
   -- p.maxshield = 0
  end