impl FromIterator<()> for ()

impl FromIterator<()> for ()

This just collapses all unit items from an iterator into one.  This is
more useful when combined with higher-level abstractions, like
collecting to a `Result<(), E>` where you only care about errors:

```rust
use std::io::*;
data = vec![1, 2, 3, 4, 5];
let res: Result<()> = data.iter()
    .map(|x| writeln!(stdout(), "{}", x))
    .collect();
assert!(res.is_ok());
```