Feature suggestion: apply a closure to all the pixels of the map

I frequently find myself writing code to work with bitmaps that looks like this:
```
    for x in 0..map.get_width {
        for y in 0..map.get_height {
            ...
            let _ = map.set_pixel(x, y, {function call]);
        }
    }
```

Some syntatic sugar for that in the form of 
```
map.apply_to_pixels({|x, y| ...});
```
would be amazing