Stream-python

* Handle backward compatible pyjwt 1.x support for token generation

* Add analytics support for `track_engagements` and `track_impressions`
* Update license to BSD-3 canonical description

* Bump pyjwt to 2.x

* Drop python 3.5 and add 3.9
* Improve install and CI

* Drop old create_user_session_token in favor create_user_token
* Drop python support before 3.4
* Allow custom data in client.create_jwt_token
* Add kind filter for reactions in enrichment
* Add follow stat support
* Move to github actions from travis and improve static analysis
* Update readme for old docs
* Update some crypto dependencies

* Handle warning in JWT decode regarding missing algorithm