More bug fixes and SFX!

There's a bunch of rough edges I ironed out yesterday. Here's a list of fixes and additions!

• FIX - Units will no longer heal from dead. Instead, there is a revive ticker in place of healing, and the unit will revive once the revive ticker is full.
• FIX - Enemies will no longer target knocked out heroes.
• ADD - SFX and corpse for Wraith death.
• ADD - SFX and corpse for Skeleton death.
• ADD - "Downed" state for the swordsman. He'll kneel over when he's knocked out and waiting for revive.
• CHANGE - Changed music to something more ambient (Digital Illusions from PMSFX). Still not final, but hopefully more fitting!

Getting the submission ready for conferences, but hopefully back to feature work soon. I'm really excited about adding traps, another hero, three more enemies, and a first level boss!

On the point of adding another hero, I'm still undecided whether 3 is the magic number to have. The new one will be a ranged hero with targeted sniping abilities. Let me know if you have any suggestions!