normalize method
Implementation
Quaternion normalize() {
var l = length();
if (l == 0) {
_x = 0;
_y = 0;
_z = 0;
_w = 1;
} else {
l = 1 / l;
_x = _x * l;
_y = _y * l;
_z = _z * l;
_w = _w * l;
}
onChangeCallback();
return this;
}