code: def combine_bam(in_files, out_file, config):
      
      runner = broad.runner_from_path("picard", config)
      runner.run_fn("picard_merge", in_files, out_file)
      for in_file in in_files:
          save_diskspace(in_file, "Merged into {0}".format(out_file), config)
      bam.index(out_file, config)
      return out_file
docs: Parallel target to combine multiple BAM files.