Create text files of the dispersion curves for each spin system.
dir: The directory name to place all of the spin system files into.
force: A flag which, if set to True, will cause the files to be overwritten.
This is used to created text files of the dispersion curves of R2eff/R1rho values, both measured and back calculated from the optimised dispersion model. The columns of the text file will be the experiment name, the magnetic field strength (as the proton frequency in MHz), dispersion point (nu_CPMG or the spin-lock field strength), the experimental R2eff value, the back-calculated R2eff value, and the experimental R2eff error. One file will be created per spin system with the name `disp_x.out', where x is the spin ID string.