Improved comments on find_offset and renamed a variable to be more descriptive.
Removed an unused variable in state_point.F90
More comment improvements. More style improvements.
Updated docs for _get_offset
Moved score_surface_current.
Improved comments and variable names in calc_offsets.
Changed count_target_cell/univ to functions.
Fill cell bug fix.
Only calculates offsets for each universe once.
Removed track_xyz. Moved cross_surface back to geometry.F90. Removed geometry dependency from tally.F90. Added mapping vector to particle_header. Offset now tracked in find_cell and cross_lattice.