``ClassName -> class_name.html``.

def _get_file_name(tlobject):
    """``ClassName -> class_name.html``."""
    name = tlobject.name if isinstance(tlobject, TLObject) else tlobject
    # Courtesy of http://stackoverflow.com/a/1176023/4759433
    s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    result = re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower()
    return '{}.html'.format(result)