move country data to its own JSON file (fixes #2)

Some thoughts on this block.
Constructors with empty arg lists don't need parens. :eggplant: 
The third argument to `XMLHttpRequest.prototype.open` is optional, defaults to true, you may omit it.
The third argument to EventTarget.addEventListener is optional, defaults to false, you may omit it.
No need to log on error.
If you set the responseType attribute of the XMLHttpRequest instance, you shouldn't need the ```try { JSON.parse } catch` block below.
:eggplant:  :eggplant:  :eggplant: