ne_50m_admin_0_countries

Adding features from [`ne_50m_admin_0_countries.geojson`](https://github.com/nvkelso/natural-earth-vector/blob/master/geojson/ne_50m_admin_0_countries.geojson).

Command:

> wp --url=bgeo.me --require=./bgeo-data.php bgeodata simplify_and_correlate naturalearthdata/ne_50m_admin_0_countries.geojson --namekeys=admin,sovereignt --woetypes=12