major rebalances

10s generator is too slow -- 10 seconds ago is an eternity in a shmup
and a player who has stopped firing should recover much faster. The
generator's max capacity is much lower and shield cost has been
rebalanced to match.

The Protron is much more expensive to fire, it was previously just
easy mode.

Shields now recover faster _once they start recovering_ (every second
if energy is available) but getting hit causes a "penalty cooldown"
that is much longer than the standard recovery interval. This behavior
is taken from Halo and basically every modern FPS that came after it;
it's unlike Tyrian, which had consistent shield recovery behavior.
But I think Halo's rule plays much better.

vacuum_gambit.p8

@@ -413,13 +413,12 @@ ship_m = {
  shield = 0,
  maxshield = 0,
  shieldcost = 32767.9,
- shieldcooldown =  0x0.00a0,
+ shieldcooldown =  0x0.003c,--1s
+ shieldpenalty = 0x0.012c, --5s
  
- -- default generator behavior:
+ max_power = 120,
- -- 10 seconds for a full charge
+ power = 120,
- max_power = 600,
+ generator = 2, -- power gen per frame
- power = 600,
- generator = 1, -- power gen per frame
  
  slip = true,  -- most enemies slide
  
@@ -538,7 +537,7 @@ end
 
 function ship_m:hitsomething(dmg)
  if (dmg <= 0) return false
- self.shield_refresh_ready = lframe + self.shieldcooldown
+ self.shield_refresh_ready = lframe + self.shieldpenalty
  if self.shield >= dmg then
   self.shield -= dmg
   self:ow(true)
@@ -772,7 +771,7 @@ mknew(protron)
 protron_gun = gun_base.new{
  icon = 25,
  enemy = false,
- power = 35,
+ power = 60,
  cooldown = 0x0.000f, -- frames between shots
  ammo = nil,
  maxammo = nil,
@@ -876,8 +875,8 @@ player = ship_m.new{
  maxhp = 3, -- player only; other ships never heal
  shield = 2, -- regenerates, using power
  maxshield = 2,
- shieldcost = 300, -- power cost to refill shield
+ shieldcost = 60, -- power cost to refill shield
- generator = 1.5,  -- 1 feels too slow
+ generator = 2, 
 
  -- gun
  main_gun = nil, -- assign at spawn time
@@ -1569,10 +1568,12 @@ shields - ship.shieldcost per
 point of shields. shieldcooldown
 is the interval between
 restoring shield points, which
-is reset when a ship takes
+is reset to shieldpenalty when a
-damage (regardless of whether
+ship takes damage (regardless of
-that damage is stopped by the
+whether that damage is stopped
-shield or not).
+by the shield or not).
+shieldpenalty is much worse than
+shieldcooldown (hALO shield).
 
 therefore:
 * damaged ships spend power