Blank line between doc comment or outer attr and the thing it's attached to

[joshtriplett]

/// item comment for main

fn main() {
    println!("Hello, world!");
}

I would expect the blank line to get removed, but it isn't. I think we should fix this over a style edition.

@traviscross pointed out that the same thing applies to outer attributes:

#[attribute_for_main]

fn main() {
    println!("Hello, world!");
}

I think we should normalize this case to zero blank lines, as well.