Release v1.0.3

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[1.0.3] - 2023-10-03

Updated dependencies, moved source code to src, made Ruff rules stricter,
and fixed outdated Makefile.

Added

• Added new rules for Ruff
• Added hash support for the Date class

Changed

• Moved the source code files under src to better match accepted best
  practices
• Updated outdated links in CHANGELOG.md
• Updated dependencies
• Updated localisation files

Fixed

• Fixed Makefile's linting (it was still using pyproject-flake8
  instead of Ruff)
• Various linter fixes
• README.md had an old version number for Python, this is now fixed