pub fn flip_vertical<P>(image: &Image<P>) -> Image<P>
where
    P: Pixel,
{
    let mut out = image.clone();
    flip_vertical_mut(&mut out);
    out
}
Vertically flips an image.

# Examples
```
use imageproc::compose::flip_vertical;
use imageproc::gray_image;

let image = gray_image!(
1, 1, 1, 1, 1, 1;
2, 2, 2, 2, 2, 2;
3, 3, 3, 3, 3, 3;
4, 4, 4, 4, 4, 4;
5, 5, 5, 5, 5, 5;
6, 6, 6, 6, 6, 6);

let flipped = flip_vertical(&image);

assert_eq!(flipped, gray_image!(
6, 6, 6, 6, 6, 6;
5, 5, 5, 5, 5, 5;
4, 4, 4, 4, 4, 4;
3, 3, 3, 3, 3, 3;
2, 2, 2, 2, 2, 2;
1, 1, 1, 1, 1, 1));
```
src/compose.rs