Moved Watt and Maxwell spectrum sampling to math module.
Moved transport subroutine to new tracking module. The physics module now does not dependent on the geometry or tally module.
Get rid of OBJECTS file and use Makefile wildcard function instead.
Remove dependence of elastic_scatter on particle.
Remove dependence of inelastic_scatter on particle.
Remove dependence of sab_scatter on particle.
Remove dependence of sample_target_velocity on particle.
Changed rotate_angle into a function.
Move clearing of surface before collision to tracking module.
Removed index_grid and interp components of Particle. Simplified find_energy_index.
Particle is no longer global. initialize_particle moved to particle_header.
Created new scatter subroutine that covers elastic, inelastic, sab.
Always sample cdf for scattering. Random number stream will change!
Added russian_roulette subroutine.
Added sample_nuclide function.
Enhance sample_nuclide to work for total material scatter and fission.
Changed absorption estimate of k to use microscopic cross sections.
Refactored fission and disappearance reactions. Random number sequence will change.
Removed unused variables in physics module.
Merge branch 'master' into refactor