v0.2.4

• Add option to subset a grid with a shape file (OGRGeometry) in
  get_shp_grid_points.
• Add shapefile module for reading shapefiles from
  http://biogeo.ucdavis.edu/data/gadm2.8/gadm28_levels.shp.zip by Global
  Administrative Level
• Ensure that get_bbox_grid_points returns points while taking cell order into
  account.