Add two letter country codes to :locations according to ISO_3166-1

[Bost]

How to pull the country codes as JSU doesn't offer them. I'm guessing the best solution would be to hard-code them into a map (e.g: "Mainland China" => "CN"), the issue here would be to update the code if JSU decides to use a different key when they add new countries.

See the comment at country_name_synonyms and the country_code docstring.
(We might want to add that explanation to the README.md)

[ExpDev07]

Exactly something like this I was thinking about. Very good work! Is this neccecary:?
pip install --upgrade flask-cors python-dotenv requests cachetools python-dateutil

Running "pipenv install" in the directory should be enough to install the dependencies?

[ExpDev07]

Remove pip install --upgrade flask-cors python-dotenv requests cachetools python-dateutil as it's not necessary if you've properly installed dependencies using pipenv install.

Also change countrycode to country_code to comply with the JSON API specification.