Feature request: Vectorial quantities (e.g. p. velocity and active intensity spherical harmonics components)

[xefonon]

Hello again! Another feature I could add would be the vectorial quantities of particle velocity and intensity components (angular and radial) from a spherical harmonics expansion of a sampled pressure field according to ref [1].

[1] Williams, Earl G., and Kazuhiro Takashima. "Vector intensity reconstructions in a volume surrounding a rigid spherical microphone array." The Journal of the Acoustical Society of America 127.2 (2010): 773-783.