Implement C++ modernization changes to EvtGen.
First major revision incorporates [[ https://gitlab.cern.ch/lhcb/Gauss/merge_requests/382 | updates ]] from Gerhard Raven (LHCb) with the initial import of all changes made to the [[ https://phab.hepforge.org/rEVTGENb240d9114f86 | modernize branch ]]
Ongoing work continues, including multithreading updates.