abe-for-sas v2.0

SAS macros for augmented backward elimination as published in
Dunkler D, Plischke M, Leffondre K, Heinze G: Augmented Backward Elimination: A Pragmatic and Purposeful Way to Develop Statistical Models. PLoS ONE (2014) 9(11):e113677 DOI:10.1371/journal.pone.0113677.