Update to version 1.3.0

Summary of changes:

• inhomogeneous material parameters
• extract data along curves
• new sample visualization
• added calculation of mode linewidths
• 5 new examples
• 3D confined samples and antiferromagnets (experimental)
• other

Detailed patch notes are found at https://tetrax.readthedocs.io/en/latest/release_notes.html#version-1-3-0