Finds the <title> for the given HTML file, or (Unknown).

def _find_title(html_file):
    """Finds the <title> for the given HTML file, or (Unknown)."""
    # TODO Is it necessary to read files like this?
    with html_file.open() as f:
        for line in f:
            if '<title>' in line:
                # + 7 to skip len('<title>')
                return line[line.index('<title>') + 7:line.index('</title>')]

    return '(Unknown)'