KillCallback

Adds a client sided callback triggered each player kill in the match.

Note:

Thanks to Fifty#8113 and Spoon#1812 as they did most of the work on this, I just put it together and made it into a mod.

For end users:

This alone does nothing but is required for other mods to function.

If another mod listed this one as its dependency, download it!

For modders:

`AddCallback_OnPlayerKilled( void functionref( entity victim, entity attacker, int damageSourceId ) callback )`

Note: this is triggered each time a player gets killed in a match, not just by the client player. If you only care about client player's kills, simply check if attacker == GetLocalClientPlayer()

Any mods using this should have their priority higher than 1.