add RG/PM header tag - closes #179
add RG/PM header tag - closes #179

bioinformed/pysam,bioinformed/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,pysam-developers/pysam,bioinformed/pysam,kyleabeauchamp/pysam,bioinformed/pysam,dannon/pysam,kyleabeauchamp/pysam,dannon/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,bioinformed/pysam,dannon/pysam,dannon/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,dannon/pysam,TyberiusPrime/pysam,pysam-developers/pysam,kyleabeauchamp/pysam