Pycountry -> country_convertor

[brynpickering]

Fixes #58

Reviewer checklist

• There are no pip dependencies in the module's environment files (workflow/envs/).
• All rules use pathvars (e.g., <results>) in their inputs and outputs.
• The integration test-suite is successful, including:
  • pre-commit.ci tests pass.
  • tests pass for all relevant OS configurations (linux, osx, windows).
• Module documentation is up-to-date, including:
  • INTERFACE.yaml mentions all relevant pathvars and wildcards.
  • README.md describes how to use the module and has the necessary citations.

[irm-codebase]

Thank you for the submission Bryn!
Looks good to me 🛩️

[irm-codebase]

@all-contributors please add @brynpickering for code

[allcontributors]

@irm-codebase

I've put up a pull request to add @brynpickering! 🎉