assign CA/CB peaks in sequence-specific-assigned SS as being i or i-1 peaks based on chemical shift matching between sequential SS
clean up sequential SS chain:

 - add peaks where necessary as determined by i/i-1 peaks in
   sequentially matching SS, also placing them into the
   appropriate SS
 - assign i/i-1 of peaks based on SS matching
 - retag peaks if mistagged based on SS matching