Nullable!T

[Adam Ruppe]

I said:
> Blargh, what I'd want is
> if(x is null)

Then went off and implemented something where that doesn't actually
compile, and forgot to mention it.

This is the reason I used a T* in the nullable struct; I was hoping to
take T* is null and make it work for the struct as a whole, but it
didn't work. (tried alias this).

But I dropped it and got everything else to work, so it isn't all bad,
I just forgot to mention this.

It would still be nice if x is null could be gotten to work here. It
wouldn't feel complete without it.