Before, to have a custom function, you needed to use the Java API to register it. It's not mandatory anymore. All USS scripts put into the ./functions/ folder will be a callable function in your spells. Check the related documentation for more details about the parameters and output syntax.
Allies system. When playing with friends, you don't want your summoned monsters to attack them.
Created a provider (Java API) to register custom allies relationships. For example, if you have a homemade plugin to handle parties, you will be able to say if two entities are allied.
For now, the only "allies" test is using the vanilla Teams systems : entities in the same scoreboard team with disabled friendly-fire will be considered as allies. More allies-conditions will be added later.
New properties
can_damage_caster used by projectiles. Control if a projectile can damage its own caster.
can_damage_allies : the same as before, but with the caster's allies.
can_aggro_allies : the same as before, but for standard summons, not projectiles.
In a future version, those properties names may change to clarify them.
New function
are_allies(Entity, Entity) -> Boolean : check if two spell-entities are allies.
Other changes
The players scope will now accept a bukkit entity if it has a player scorebard tag attached to it. Thus, NPC can now be included in this scope with spells.
(technical) The projectile damage was using NBTs. It's not the case anymore.