A particle action is some function that is triggered by some event.
Right now, users cannot control this. There is just a
randomize-velocity on-birth action. So the direction of spawned
particles is slightly randomized now.
This also adds a new integer attribute called "Hash" which is
useful for a number of things. Mainly for generating random numbers
for a specific particle. The ID of a particle is not necessarily a good source
of randomness.
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