Client Python 3.2.0

What's Changed

Bumped version to 3.2.0a1 by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/105
Upgrade fastavro to 1.7.3 by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/110
Update to bookkeeper client 4.16.1 by @merlimat in https://github.com/apache/pulsar-client-python/pull/111
[Doc] Add links to client docs and feature matrix in README.md by @momo-jun in https://github.com/apache/pulsar-client-python/pull/117
Bump the C++ client to 3.2.0 by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/118
Add docs and tests for AuthenticationOauth2 by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/120
Make acknowledge APIs synchronous and improve the documents by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/121
Use readNextAsync for reader.read_next() by @merlimat in https://github.com/apache/pulsar-client-python/pull/125
Release the GIL before any call to async methods by @merlimat in https://github.com/apache/pulsar-client-python/pull/123
Fetch writer schema to decode Avro messages by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/119
Include the C extension when generating API docs by @BewareMyPower in https://github.com/apache/pulsar-client-python/pull/126

Full Changelog: https://github.com/apache/pulsar-client-python/compare/v3.1.0...v3.2.0