ParticleEffects: improve particle position randomizer algorithm

[meszaros-lajos-gyorgy]

Using sin() for calculating the values of s vector will only fill half of the circle around the center, cos() goes into the negative territory aswell.

A little illustration on how it works incorrectly in current versions of arx:

[gr4viton]

Clever!

[Proletar666]

Is the project still alive? I was eagerly waiting for a new release but it seems Arx Libertatis is dead.