Created R script to encode countries into ISO3 standards.

Used the `countrycode` R package to encode the `country`, `subject`,
`category` columns into the iso3 standard. I created three new columns
as an output and added it to the cleaned data.frame. The new columns
need to be compared to create a new one. Based on eyeballing it seems
that the `countrycode` is encoding correctly around 90% of the entries.

(Sorry for the sloppy code and bad commenting. I will try to improve it
sometime today or tomorrow.)