Add `fn item<T>(x: T) -> Item<T>` function

[brendanzab]

Some(x).into_iter() is a handy idiom when chaining iterators together. It would be nice to have a shortcut function defined as:

use std::option::Item;

fn item<T>(x: T) -> Item<T> {
    Some(x).into_iter()
}

[Gankra]

Does it need to be in the prelude?

[sinistersnare]

If it wasnt in the prelude, then it would be easier to just type in Some(x).into_iter() I guess.

I feel like this is just feature creep, and not necessary.

[brendanzab]

I have wanted this before, and think it would be useful, but I'll close this for now...

[reem]

I would like there to just be a special Singleton iterator in std::iter, which, while less convenient to access than Some(x).into_iter() would be much easier to understand.