Allow changing Fano factor
This MR allows changing the Fano factor to simulate the fluctuations in the number of electron-hole pairs created from a given amount of energy deposited in the material.
The following changes have been made:
- Fluctuations using Fano factor with Gaussian statistics on energy deposition
- Added test case to see change in e/h pairs created
- Adapt test cases to changed seed distribution
- Added references to the manual for Fano factor used and average ionization energy