How to serialize a double.

[Jake Pittis via Digitalmars-d-learn]

How do I convert a double to a ubyte[]?

I've tried all sorts of things including converting the double to 
a ulong and trying to serialize the ulong. For example test 
bellow fails.

````
unittest {
    double d = 3.14;
    ulong l = *cast(ulong*)(&d);
    double after = *cast(double*)(&l));
    assert(after == d); // This fails.
}
````