{AH} add build_reference_sequence function
{AH} add build_reference_sequence function

pysam-developers/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam