Added MaxCombatDistance Tag (cannot damage boss if you are further away
than the specified distance).
Added Effect skill and "Sound" effect to go along with it, will add more
effects in the future... sound effect plays a sound from the resource
pack.

Usage:
  - effect TARGET EFFECT effectoptions >0 1
  
Target can be boss or player right now.
  
Sound effect has options path.to.sound:volume:pitch

Example:
  - effect boss sound mob.zombie.say:2:2 >0 1