Make working with NonZero Nicer

[Keith-Cancel]

It would be nice if there was some way to express things like this.

// There is `ZeroablePrimitive` but that is an unstable and internal trait.
struct Example<U: PrimInt> {
    nz: NonZero<U>,
    val: U
}

I don't see anything really in the num_traits for working with NonZero or knowing that the type can be made into one.

// I ended up doing something like this:
struct Example<U: PrimInt + NonZeroType> {
    nz: U::NonZero,
    val: U
}
// However this leaves a lot traits and other features of NonZero not available
// short of adding more to this trait
pub trait NonZeroType: PrimInt {
    type NonZero;
    fn new(self) -> Option<Self::NonZero>;
    unsafe fn new_unchecked(self) -> Self::NonZero;
    fn get(nz: Self::NonZero) -> Self;
}