Function pad 

pub fn pad<T: Image>(
    top: usize,
    bottom: usize,
    left: usize,
    right: usize,
    padding: T::Pixel,
    frame: T,
) -> Pad<T>

Uses the given pixel to pad a frame.

The result will have a width of left + frame.width + right and a height of top + frame.height + bottom.