[VEX] centroid in vex

-------calc centroid
vector min, max;

getbbox(min, max);
vector center = (min+max)/2;
 
Thx for reference!! 
 https://forums.odforce.net/topic/21514-centroid-in-pointwrangle/

-------fit bottom of model to origin

vector min, max, center;
getbbox(min, max);
center = (min+max)/2;

@P -= center;
@P.y += (max.y - min.y)/2;