improved build_StatMat_TravIns to do the sequences of zeros much more efficiently
minor
minor
changed differential_coords_finder to differential_coords_finder_ints_guaranteed,
which only accepts integers as its final two arguments. That's all I need.
changed some shitty acronyms
fixed a dodgy usage of diff_upgr which causes it to get the differential number wrong
fixed up a continuing error with the calculation of differential numbers
minor
minor
minor
minor
changed a couple of sums to adds