minor changes to UserSession
minor changes to UserSession

- Got rid of the base class that was meant to act as an interface
- Added docstrings to all public methods
- Modified logout to make a request with a callable that provides the header required for the logout endpoint to succeed

looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen,looker-open-source/sdk-codegen