The mathfunctions expanded with a function that calculated the derivative.

The Energy spectrum function somewhat optimised. However a bug remains the r_shell function that it gives a to small dr.
Repaired the Mathfunctions. The step is now not zero.

Added in main that the spectrum is printed to file.

Spectrum file is a bit debuged but not enough
added a function for the outward going ions, This function is not fully tested.
added that the spectrum functions also calculate the spectrum inside the fusor.

However by implementing that the spectrum on diverend radii is printed to a file the code hangs on unexpected radii.