cleans up implementation of PP tool parameter

cpp/full_code/NSVE_field_stats.cpp

cpp/full_code/NSVE_field_stats.hpp

cpp/full_code/bandpass_stats.cpp

cpp/full_code/bandpass_stats.hpp

cpp/full_code/check_divergence.cpp

cpp/full_code/check_divergence.hpp

cpp/full_code/get_3D_correlations.cpp

cpp/full_code/get_rfields.cpp

cpp/full_code/get_velocity.cpp

cpp/full_code/joint_acc_vel_stats.cpp

cpp/full_code/pressure_stats.cpp