Legacy IGRF source code updated to use IGRF-13 model data.
Latest IGRF-13 coefficients defines coefficients up to 13th order and provide them in single table form, also fortran source code provided with new coefficients ommited almost all earlier available functions to calculate L-shell and B0 parameter.
igrf_sub.for provided in this repository is modified to be able to process coefficients up to 13th order. Also simple python script convert-data.py is provided to convert data from single table form to several *.dat files.