The relaxation and magnitisation data structures are now initialised with the target function
initialisation, rather than being created at each target function call. The Rex and M0 matrices are
now updated at the base of the target function rather than in the lib.dispersion.ns_2site_star
module to minimise the number of mathematical operations per target function call. And the M0
matrix has changed shape and a dot product is used in lib.dispersion.ns_2site_star to create Moft
instead.
