Version 5.2.0 - Introducing RestTokensManager class

Along with some bugfixes and updates to examples, 5.2.0 adds the RestTokensManager class to the base distribution. There is an example of it being used called limited_rest_api_wrapping_tableau_rest_api.py which shows in action. README needs to be updated to reflect its full functionality. This is based on best practice implementation of a single process web application like Django needing to request things like Workbooks for individual users.