Feature request: Sound field separation of incident and scattered components with rigid sphere

[xefonon]

Hello! Thanks for a really cool repo. I could contribute a few things which I feel belong here and I can't really find them in many places on github, like the separation of incident and scattered components of a sound field with a rigid sphere interfering.

This would include:

• a function which returns the incident and scattered components of pressure based on the analytic expressions derived in Appendix A of ref [1]

[1] Fernandez-Grande, Efren. "Sound field reconstruction using a spherical microphone array." The Journal of the Acoustical Society of America 139.3 (2016): 1168-1178.