Particle splitting tracking

Implements a binary tree to track particle splits.

So far in this initial version I have only created an example, and the infrastructure to perform this tracking with SPHENIX.

I also have to write out the values as longlongs, as it doesn't appear that the conversion i/o routines allow for the use of UINT8 and longs? I don't fully understand how this magic works, so if @matthieu has any ideas I would appreciate it.

The example produces this plot, which shows which particles were split from which others (arrows point from the particle that remained to the particle that was split off from it). In the example we take an initial mass of 16x what is expected, which is then split 4 times.

If we are happy with this implementation, I can go ahead and make the required changes for stars, black holes, sinks, and the other hydro schemes.