Ready for review & merge @luizirber @camillescott @ctb

• Is it mergable?
• Did it pass the tests?
• If it introduces new functionality in scripts/ is it tested?
  Check for code coverage.
• Is it well formatted? Look at make pep8, make diff_pylint_report,
  make cppcheck, and make doc output. Use make format and manual
  fixing as needed.
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Is it documented in the ChangeLog?
• Was a spellchecker run on the source code and documentation after
  changes were made?

LGTM. See: https://pip.pypa.io/en/latest/user_guide.html