Issues related to the description of region and box parameters

[chenyqmy]

Hello, mdtanker: In the documentation of polartoolkit, I noticed that you describe the region parameter in the format of [e, w, n, s]. For example, in the region_xy_to_ll function. However, I find that this region parameter should be in the format of [xmin, xmax, ymin, ymax], which is also the default -R option in GMT. I think in the EPSG:3031 coordinate system, the [e, w, n, s] format may not be the proper description, and it could be a bit confusing. Moreover, in GMT, the [W|E|S|N] format is the way to specify the region. I wonder if there's a mistake in this, and I could be wrong. Your package is very useful. Thank you for your work.