TODO

dd. 10 may 2022
Test the functions En, In and Kn - based on recurrence relations. Implementation DONE - needs to be checked

Check the function inverse_chi - strange jump at x = 3.

Check the function integral_spence - results differ from Mathworld.

Convert double precision and complex versions in the same way.

dd. 17 may 2022
Convert the Bessel functions of fractional order. Besks. DONE

Implement relations for the derivatives of Bessel functions. DONE - needs to be checked

dd. 22 may 2022
Add test programs for the extra Bessel functions and the derivatives.

Make sure that the module for complex functions does not cause conflicts
with the other modules.