pub fn find_contours<T>(image: &GrayImage) -> Vec<Contour<T>>
where
    T: Num + NumCast + Copy + PartialEq + Eq,
{
    find_contours_with_threshold(image, 0)
}
Finds all borders of foreground regions in an image. All non-zero pixels are
treated as belonging to the foreground.

Based on the algorithm proposed by Suzuki and Abe: Topological Structural
Analysis of Digitized Binary Images by Border Following.
src/contours.rs