Type parameters on statics

Would this be possible?

``` rust
pub enum Reply<V, StopReason> {
    Reply(V),
    Stop(StopReason),
}

pub static Continue<StopReason>: Reply<(), StopReason> = Reply(());
```

I guess it would be less useful than the [C++14 proposal](http://isocpp.org/files/papers/N3651.pdf) seeing as our constexprs are currently so limited.
