First try to implement function that will calculate the matrix exponential by striding through data.
Interestingly, it does not work. Theses systemtests will fail.
test_hansen_cpmg_data_to_ns_cpmg_2site_3D
test_hansen_cpmg_data_to_ns_cpmg_2site_3D_full
Task #7807 (https://gna.org/task/index.php?7807): Speed-up of dispersion models for Clustered analysis.
