CRAN Version 1.3.0

[nathansam]

Code changes

Tests have been refactored: making it easier for others to contribute their own
tests. See #57.

Documentation

• Now discuss more R packages similar to datefixR in README
• Warnings and errors have been translated to German thanks to Daniel
  Possenriede (@dpprdan on GitHub)
• Fixes typo in README for the German language (now "Deutsch")

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This discussion was created from the release CRAN Version 1.3.0.