variance

auto a = [ 1.0f, 1, 1 ];
assertEq( a.variance, 0.0f );

auto b = [ 1.0f, 2, 3 ];
assertEq( b.variance, 1.0f );

import des.math.linear.vector;

auto a = [ vec3(1,2,3), vec3(2,3,4), vec3(3,4,5) ];
assertEq( a.variance, vec3(1,1,1) );