Small improvements

[dbrakenhoff]

• Load ds from binary model grid (e.g. model.disv.grb file)
• Improve pyproj CRS initialization
• Add get_area() method using shoelace formula
• allow plotting modelgrid with or without rotation.

[rubencalje]

Looks good. Would add_area_to_ds not be a better method name, instead of get_area?

[OnnoEbbens]

I think it is better to return the area and not add the area to the dataset. Like we do in get_idomain. Also discussed in this issue #254