Handle countries history

[noirbizarre]

Right now there is only the latest country borders published by Natural Earth and countries does not have a time related identifier.

In order to be uniform and a little bit exhaustive, it would be nice to handle time on countries.

Here some potential sources:

• http://nils.weidmann.ws/projects/cshapes.html
• https://mapzen.com/blog/who-s-on-first/