Minor Release: v3.1.0

[ma-sadeghi]

🚀 New features

• Added wrapper for pyamg.ruge_stuben_solver to openpnm.solvers

🍰 Enhancements

• Fetching 'pore.source' from an algorithm without any source terms defined returns empty dict instead of KeyError

🔧 Maintenance

• Removed the use of py from unit tests
• Switched CI linter from pycodestyle to flake8
• Fixed numerous style errors throughout to satisfy flake8

📗 Documentation

• Enhanced some example notebooks, added a new notebook on managing clustered networks

---

This discussion was created from the release v3.1.0.