Return the BAM/SAM header
        
        Returns
        -------
        generator
            Each line of the header

def header(self):
        """
        Return the BAM/SAM header
        
        Returns
        -------
        generator
            Each line of the header
        """
        
        cmd = [self.__samtools, 'view', '-H', self.__bam]

        stdout = subprocess.Popen(cmd, stdout=subprocess.PIPE).stdout

        for l in stdout:
            yield l.decode('utf-8').strip()

        stdout.close()