Fastapi-sso

Added support for login using Fitbit.

- kakao support (contributed by Jae-Baek Song - [thdwoqor](https://github.com/thdwoqor))

- `params` argument (allows to specify `access_type: offline` etc.
- `scope` argument for `SSOBase` constructor
- fix typo in docs
- move examples to [`examples/`](examples/)

Allow specifying `redirect_uri` on request time.

do not force body on GET request

Use `httpx` instead of `aiohttp`