* Added base funtionality for PKCE Authorization - i538
* fixed a mistake with the auth code
* fixed more misunderstandings. fixed grant_access_token to now call authorization if needed
* added comments and references to code verifier and code challenge
* removed debug print statement
* updated unit tests for new PKCE flow
* cleaned up username issues - added doc strings to class
* fixed import issue, added user endpoint tests
* forgot to commit this file
* linted
* clarified comment
* no longer generates code verifier or challenge in constructor, only when needed
* fixed flake8 complaints, added forgotten unit tests
* fixed linting with unit tests
* anotha one
* added python3.5 support
* linting
* added to CHANGELOG
* removed as_dict option from get_access_token()
Co-authored-by: tomCLANCC <26153156+tomCLANCC@users.noreply.github.com>
