…,the Expires of cookies will always be 'Session' which means that the cookie will be expired when the browser closed(or close tabs).In this situation,timeout of the session is meanless.Now,with the modify we can set a value of seconds in web (via select of other things) make cookie stored in clients for a period.

* Remove py2.3 support.
* Replace `attr in obj.keys()` by `attr in obj`.
* Set default cookie expire time to session timeout.
* Add support for SameSite cookie.

Fixes #521
Fixes #61 #99 #337
Fixes #409 #410