Plague 3.10

• additional sprite art from Sean Lange
  
• made zombie_hive counter decrease when zombie_hives destroyed
  
• fixed creation of remains – this crashed python when uninfected humans were killed
  
• added a timer to ai to make sims pick another destination after a few seconds (stops them getting stuck indefinitely)
  
• added comments to sim “add sight tiles” code
  
• (last version, whoops!) made it so that health and ammo “tick up” as you stand over them, no longer instant refills
  
• increased animal burn_max so that zombies and survivors burn for a little longer