function squaredDistance(a, b) {
    var x = b[0] - a[0],
        y = b[1] - a[1],
        z = b[2] - a[2]
    return x*x + y*y + z*z
}
Calculates the squared euclidian distance between two vec3's

@param {vec3} a the first operand
@param {vec3} b the second operand
@returns {Number} squared distance between a and b