Methods to replace math domain errors in model ns_cpmg_2site_3d, has been replaced with numpy masks.
number of points has been removed, as the masks utility replaces this.
pB is now moved to be calculated inside. This makes the lib function simpler.
k_AB and k_BA is also now calculated here.
Magnetization vector is also now filled in lib function.
Task #7807 (https://gna.org/task/index.php?7807): Speed-up of dispersion models for Clustered analysis.
