Some better error messages

[opfromthestart]

What does this PR accomplish?

Makes error messages more readable

• 🩹 Bug Fix
• 🦚 Feature
• 📙 Documentation

Closes #182 .

Changes proposed by this PR:

This replaces some operations that can fail with better error messages

Notes to reviewer:

Unsure of how to test this per se, since it is based on errors. I don't know all the places it could go wrong, so I need help with identification.

📜 Checklist

• [ ] Add explicit bounds checks when needed
• [ ] Add help messages for common errors
• [ ] Test coverage is excellent
• [ ] All unit tests pass
• [ ] The juice-examples run just fine
• [ ] Documentation is thorough, extensive and explicit