normalize method
Normalize the current Quant
Implementation
Quat normalize(){
double l = length();
if ( l == 0 ) {
set( 0, 0, 0, 1 );
}
else {
l = 1 / l;
x = x * l;
y = y * l;
z = z * l;
w = w * l;
}
return this;
}