Rewrite geometry support

[philippkraft]

Follow up to #7.

With using the __geo_interface__, the cells_from_polygons function will get a complete rewrite with API change. The callables are hard to explain and ugly to use.

• But how to gain that flexibility else?
• Or is documentation enough?

[philippkraft]

Add a field string cmf::upslope::Cell::WKB in cell.h that can be loaded with a OGC-WKB representation. That WKB can be used to create Shapely-Polygons on the fly.

Creating cells and connecting cells can become two distinct jobs and cells_from_polygons would be simpler.

Challenge

How to mark a std::string as a Python byte-string? swig/swig#752

Idea:

typedef bytestring std::string;
%typemap(out) bytestring {
    $result = PyBytes_FromString($1.c_str());
}

[philippkraft]

Current usage for cell geometry now (if shapely is present):

c.geometry = feature.shape

Needed: A cell creator helper function, like:

def make_cell_from_polygon(project, polygon, z, id=None, with_surfacewater=True):
    c=p.NewCell(polygon.centroid.x, polygon.centroid.y, polygon.centroid.z, 
                polygon.area, with_surfaceswater)
    c.geometry = polygon
    if id is not None:
        c.Id = id
    return c

[philippkraft]

Use case for current API in here

[ocni-dtu]

I have not encountered any issues with the new make_cell_from_polygons.

I would appreciate if you pushed the work to PyPI.