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

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

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

let flipped = flip_horizontal(&image);

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