added num diff option
added num diff option

wltrimbl/kmerspectrumanalyzer,MG-RAST/kmerspectrumanalyzer,wltrimbl/kmerspectrumanalyzer,MG-RAST/kmerspectrumanalyzer,wltrimbl/kmerspectrumanalyzer,MG-RAST/kmerspectrumanalyzer