Function imageproc::seam_carving::shrink_width

pub fn shrink_width<P>(image: &Image<P>, target_width: u32) -> Image<P> where
    P: Pixel<Subpixel = u8> + WithChannel<u16> + WithChannel<i16> + 'static,
    <P as WithChannel<u16>>::Pixel: HasBlack, 

Reduces the width of an image using seam carving.

Warning: this is very slow! It implements the algorithm from https://inst.eecs.berkeley.edu/~cs194-26/fa16/hw/proj4-seamcarving/imret.pdf, with some extra unnecessary allocations thrown in. Rather than attempting to optimise the implementation of this inherently slow algorithm, the planned next step is to switch to the algorithm from https://users.cs.cf.ac.uk/Paul.Rosin/resources/papers/seam-carving-ChinaF.pdf.