Spotipy

Fixed

- Fixed broken examples in README, examples and doc

Changed

- Allow session keepalive
- Bump requests to 2.20.0

Fixed

- Fixed inconsistent behaviour with some API methods when
a full HTTP URL is passed.
- Fixed invalid calls to logging warn method

Removed

- `mock` no longer needed for install. Only used in `tox`.

Added

- Support for `playlist` to get a playlist without specifying a user
- Support for `current_user_saved_albums_delete`
- Support for `current_user_saved_albums_contains`
- Support for `user_unfollow_artists`
- Support for `user_unfollow_users`
- Lint with flake8 using Github action

Changed

- Fix typos in doc
- Start following [SemVer](https://semver.org) properly

Changed

- Made instructions in the CONTRIBUTING.md file more clear such that it is easier to onboard and there are no conflicts with TUTORIAL.md

Added follow and player endpoints

Python 3 fix

Fixed proxy issue in standard auth flow