* Add SpotifyImplicitGrant with get_access_token and get_cached_token (and minimum related functions)
* Add some overlooked necessary methods/values in SpotifyImplicitGrant
* Remove unsuppported functionality and make SpotifyImplicitGrant public
* Allow/Expose integration of SpotifyImplicitGrant in client
* Add Implicit Grant tests and decrease abilities of prompt_for_user_token
Remove Implicit Grant and state support from prompt_for_user_token
* Add documentation and changelog entry
* Touch up PEP8 compliance
* Ignore long line with link for flake8
* Correct changelog
* Restore compatibility with Python 2.7
* Correct help(SpotifyImplicitGrant.get_access_token)
* Remove as_dict from SpotifyImplicitGrant.get_access_token
* Combine status check functionality with implicit grant support
In oauth2.py:
* Add state checking to SpotifyImplicitGrant
* Add dedicated SpotifyStateError as subclass of SpotifyOauthError
* Moved `_get_user_input` from SpotifyOAuth to superclass SpotifyAuthBase
* Renamed `parse_oauth_response_url` to `parse_auth_response_url`
* Moved error handling into `parse_auth_response_url`
Made minor changes in tests and client.py accordingly
* Update changelog
* Trim down tests for SpotifyImplicitGrant
* Fix trailing whitespace
* test_improvements - Add __init__.py files to tests dirs so you can run all tests
* test_improvements - added helpers file, restructured tests to work without previous data and to be grouped with api type
* http_retries - Implement Retry for all requests
* Readme - Update README with contributing info
* PR Feedback - Added CONTRIBUTING.md, fixed README, fixed test
* Linting of OAuth2 mod. + update tests to detect core package path
* Tweak imports in tests + update tox ini to ignore Flake8 E501 error
* Tweak tox ini - ignore examples
* Remove `f`-string from OAuth2 mod.
* More import tweaks in core package + tests
* Update flake8 config. in tox ini - set line length limit to 99 chars.
