RUS in the era of python

The software to perform both the forward calculations as well as the inversion of resonant ultrasound spectroscopy data started at Colorado School of Mines at the Physical Acoustics Lab. This lab, now in Auckland, continued working on the code. The most recent changes are the addition of translations to python (thank you, Paul Freeman) and the addition of a notebook to generate animations of free oscillations (courtesy of Evert Duran).