Add Raster to GeoJSON Polygon via zonal.regions + marching squares

[brendancol]

There is an interesting example of the approach implemented in Rust: https://github.com/mthh/contour-rs

[brendancol]

https://gdal.org/programs/gdal_polygonize.html

[brendancol]

http://www.eecs.umich.edu/courses/eecs487/f06/sa/jmadsen.pdf

[giancastro]

@brendancol, will this issue be worked on?

[ianthomas23]

polygonize was added in PR #585 so this can be closed.