Return the "comment header" (' * ', '# ', 'rem ', '// ', '/* ').

    This header goes before the content of a start of the
    line in a replacement.

def _comment_type_from_line(line):
    """Return the "comment header" (' * ', '# ', 'rem ', '// ', '/* ').

    This header goes before the content of a start of the
    line in a replacement.
    """
    regex = re.compile(r"^{0}".format(_ALL_COMMENT))
    match = regex.match(line)
    if match:
        return "{0} ".format(line[match.start():match.end()])

    raise RuntimeError("Unable to find comment header for {0}".format(line))