DIAMOND implementation requested

[rutgerfick]

Currently, Dmipy can modularly generate most models proposed for PGSE-based microstructure imaging.

However, the DIAMOND model by Sherrer et al. [1] is a bit particular in that it uses a matrix-variate Gamma distribution - the implementation of which does not look trivial at all.

It would be great if someone could help with DIAMOND's implementation to make Dmipy's collection truly complete!

[1] Scherrer, Benoit, et al. "Characterizing brain tissue by assessment of the distribution of anisotropic microstructural environments in diffusion‐compartment imaging (DIAMOND)." Magnetic resonance in medicine 76.3 (2016): 963-977.