force more heads for rev rounds

[Frank_Stein]

What if in the absence of heads normal crew became targets?

Let's do this. I solves one of the biggest issues of this mode, and it fits thematically and mechanically.

Heads become the initial targets, then once they're gone it just picks 1-3 people as the next targets.

Maybe it's the Revs killing off people they see as traitors of the cause. Maybe you let it pick from current Revs too, and it's a purging.

The round should be over when the antags are dead, not player targets