Simplify code to handle Seg Y revsions 0 and 1 and remove magic numbers
Simplify code to handle Seg Y revsions 0 and 1 and remove magic numbers

kwinkunks/segpy,abingham/segpy,hohogpb/segpy,kjellkongsvik/segpy,NervanaSystems/segpy,asbjorn/segpy,Kramer477/segpy,stevejpurves/segpy,NervanaSystems/segpy