module documentation

This extends Quixote's session class to have auto-detection of added or changed members or values, including lists, etc.

Class Session4 This adapts Quixote's own Session class to overwrite is_dirty() so that the session instance automatically detects changes to its values or additions or removals of members.
Class Session4SessionManager We sub-class the base version because that is missing __getitem__() and has_session() unfortunately. In future these might be added to Quixote's BaseSessionManager. See https://github.com/nascheme/quixote/issues/8...