adding back files to be reviewed

include/openmc/physics_common.h

@@ -0,0 +1,16 @@
+//! \file physics_common.h
+//! A collection of physics methods common to MG, CE, photon, etc.
+
+#ifndef OPENMC_PHYSICS_COMMON_H
+#define OPENMC_PHYSICS_COMMON_H
+
+#include "openmc/particle.h"
+
+namespace openmc {
+
+//! \brief Performs the russian roulette operation for a particle
+extern "C" void
+russian_roulette(Particle* p);
+
+} // namespace openmc
+#endif // OPENMC_PHYSICS_COMMON_H