Procedure for creating a spawned particle for i-FCIQMC.
Procedure for creating a spawned particle for i-FCIQMC.

This is identical to the existing procedure, but also stores information
about the parent of the spawned particle.

hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,ruthfranklin/hande,hande-qmc/hande,hande-qmc/hande