Change custom projectile accuracy to use Gaussian random instead of Uniform random

[Norazan]

Gaussian random makes it so the projectile has a much higher chance of aiming at the target rather than to the sides (missing), regardless of the given angular diameter. Right now it uses a uniform random function which makes the sides (aka missing the target) just as likely as hitting the target. Gaussian just generally works nicer for mob projectile accuracy. NMS also uses gaussian for projectile aim.

[Norazan]

I'll tackle this soon(tm), just making a note of it.