TooManyRedirects is not properly exposed publicly

[Harmon758]

Description

544716c (#2943) added TooManyRedirects and added it as aiohttp.TooManyRedirects in the documentation.
However, it's not properly exposed publicly in __init__.py and can only be referenced as aiohttp.client_exceptions.TooManyRedirects.

Expected Behaviour

aiohttp.TooManyRedirects works, by reference to aiohttp.client_exceptions.TooManyRedirects

Actual Behaviour

AttributeError: module 'aiohttp' has no attribute 'TooManyRedirects

Reproduction Steps

import aiohttp and attempt to use aiohttp.TooManyRedirects

Environment

aiohttp 3.5.4
Also reproducible on latest master (81cc715)