Store spatial data as Geopackages

[pratikunterwegs]

This issue is to suggest that the spatial data provided with the package could be stored as a Geopackage, rather than as .Rda files.

This reduces the language-specific aspect of the data, and makes it readable from other languages as well. Alternatives include shapefiles (vendor specific) and GeoJSONs (slower loading for larger files, I think).

This change would require adding a data access function that reads in the package data, e.g. get_colombia_regions(admin_level = n), but this could be a good way to access any of the three admin levels via an argument to the function.

Happy to chat or help with this as well.