version 2.18.0
chi^2 gradient for the finite-source point-lens models. The most changes were in two classes:
- FitData - added: get_d_A_d_u_for_PSPL_model(), get_d_A_d_rho(), data_magnification, and class FSPL_Derivatives,
- Model - added: get_magnification_methods(), methods, default_magnification_method (and its .setter), and get_magnification_methods_parameters().