pub fn rotate90<P>(image: &Image<P>) -> Image<P>
where
    P: Pixel,
{
    let (width, height) = image.dimensions();

    let mut rotated = Image::new(height, width);

    for y in 0..height {
        for x in 0..width {
            rotated.put_pixel(height - y - 1, x, *image.get_pixel(x, y));
        }
    }

    rotated
}
Rotates an image 90 degrees clockwise.

# Examples
```
use imageproc::geometric_transformations::rotate90;
use imageproc::gray_image;

let image = gray_image!(
1, 2, 0, 0;
3, 4, 0, 0;
0, 0, 0, 0;
0, 0, 0, 0);

let rotated = rotate90(&image);

assert_eq!(rotated, gray_image!(
0, 0, 3, 1;
0, 0, 4, 2;
0, 0, 0, 0;
0, 0, 0, 0));
```
src/geometric_transformations.rs