move netcdf functions to their own module(s)

[twhiteaker]

cf.py has functions for reading netCDF files, while geometry/base.py has functions for writing netCDF files. This seems a bit disorganized to me. I suggest moving the netCDF functionality to nc_reader.py and nc_writer.py.

[twhiteaker]

Perhaps something like this, after renaming ncsg to ncgeom since we call it "geometries" instead of "simple geometries" in the conventions.

ncgeom/
    io/
        shapely.py
            read_shapely()
                import shapely
            write_shapely()
                import shapely
        netcdf.py
            read_netcdf()
                import netCDF4
            write_netcdf()
                import netCDF4
    __init__.py
        from io.shapely impot read_shapely
        from io.netcdf impot from_netcdf
    container.py?
    geometry.py?

[twhiteaker]

Fixed in 72ea3166c86036f3bd0283378b7ca45c96be7f32