GDAL C API in python

[changliao1025]

Several operations using purge GDAL Python api is slow due to large data size.
In some operations, I replaced them with low level GDAL C API, such as:

pDataset_in = ogr.Open(sFilename_in)
layer_name = pDataset_in.GetLayerByIndex(0).GetName()
pKwargs = ' -f "Parquet" -dialect sqlite -sql "SELECT ST_Union(geometry), ' + sVariable_in + ' FROM ' + layer_name + ' GROUP BY ' + sVariable_in + '"'
gdal.VectorTranslate(    sFilename_out,    sFilename_in,  options = pKwargs)

This will merge the cell-based polygon to subbasin-based data for easy visualization and analysis.