docs: def print_headers(head, outfile=None, silent=False):
      """
      Print the vcf headers.
      
      If a result file is provided headers will be printed here, otherwise
      they are printed to stdout.
      
      Args:
          head (HeaderParser): A vcf header object
          outfile (FileHandle): A file handle
          silent (Bool): If nothing should be printed.
          
      """
      for header_line in head.print_header():
          
          if outfile:
              outfile.write(header_line+'\n')
          else:
              if not silent:
                  print(header_line)
      return