Hit events are written to file.

When a hit happens, the output is written out to a file (typically
hits.out).  The original particle energy and the energy deposited in the
detector are recorded.

Current issue:  Have 1 keV neutrons causing 763 keV to be deposited into
the detector after colliding with a triton (tritium) particle.

Signed-off-by: JP-Ellis <coujellis@gmail.com>