Documentation for `Session.created` does not match actual behavior

[FeldrinH]

The documentation for Session.created states that this field represents "Creation UNIX TIMESTAMP, the value returned by time.time() for very first access to the session object."

This appears to be incorrect. In practice, Session.created seems to contain the timestamp of the last time the session data was changed. There is also some inconsistency to this. In particular, Session.created is only updated if you change the session by explicitly setting or deleting a value. Calling Session.changed() or Session.invalidate() does not update Session.created, even though these methods also change the session.

What is the intended behavior of Session.created? Please update the documentation and/or code so that the documented and actual behavior match.

[asvetlov]

I guess it should reflect creation time but at some point we broke the behavior.