Knockdown sound code

Add to bottom of .cns file after [Statedef -2] entry. If there
is no [Statedef -2] entry then just make one by adding just
[Statedef -2] as a new line and nothing more. The value = 3,10
change to the sound number used in the character's .snd file.

At one time instead of GetHitVar(fall) I used the trigger =
stateno = 5110 (the state where the character is on their
back but able to get back up). GetHitVar(fall) makes it
closer to the original games though since the sound happens
when they get hit instead of when they hit the ground.

Added note: the varset is there for multiple hit moves which
would cause the sound to get messed up if not used.

[State -2]
type = PlaySnd
trigger1 = var(9) = 0
trigger1 = GetHitVar(fall) = 1
trigger1 = GetHitVar(hitcount) < 2
trigger1 = time = 0
trigger1 = alive = 1
value = 3,10

[State -2]
type = varset
trigger1 = GetHitVar(fall) = 1
trigger1 = time = 1
trigger1 = alive = 1
var(9) = 1

[State -2]
type = varset
trigger1 = stateno < 5000
trigger1 = time = 1
trigger1 = alive = 1
var(9) = 0