function max(out, a, b) {
    out[0] = Math.max(a[0], b[0])
    out[1] = Math.max(a[1], b[1])
    out[2] = Math.max(a[2], b[2])
    return out
}
Returns the maximum of two vec3's

@param {vec3} out the receiving vector
@param {vec3} a the first operand
@param {vec3} b the second operand
@returns {vec3} out