Second class functions

It would be useful to be able to do something like

```
fn do_something(x: uN[N]) -> uN[N] { ... }

proc do_something_repeatedlyuN[N] = do_something> { ... }
```

It seems like first class functions are a pretty big change that breaks lots of abstractions, but second class (or whatever, I don't know what these classes all mean) functions would allow for a lot of proc reuse, especially if types can also be parameters to the proc.