Client handles redirect + auth (#552)

Client handles redirect + auth (#552)

* Drop sync client

* Drop unused imports

* Async only

* Update tests/test_decoders.py

Co-Authored-By: Florimond Manca <florimond.manca@gmail.com>
* Linting

* Update docs for async-only

* Import sorting

* Add async notes to docs

* Update README for 0.8 async switch

* Move auth away from middleware where possible

* Drop middleware sub-package

* Client.dispatcher -> Client.dispatch

* Docs tweak

* Linting

* Fix type checking issue

* Import ordering

* Fix up docstrings

* Minor docs fixes

* Linting

* Remove unused import