Build an improved version of reflect_loss_eckart model.
- Implement the simplification from the Jones et. al. paper.
- Build a test case that compares results to plots from Jones et. al. paper.
- Update documentation to reflect these changes.
Create Beckmann-Spizzichino model for surface loss.
Correct some errors in Eckart documentation.
Move some assumptions from waveq3d.h to GitHub Issues like.