All changes:

* Feature: Support the `store.touch()` method to allow for extending the life time of a session without changing the data of it. This enables setting the `resave` option to `false`, which is recommended to avoid a session extender save overwriting another save that adds new data to the session. More info in the express-session readme: https://github.com/expressjs/session#resave
* Fix: Relax the engine requirements – accept newer versions of Node.js/iojs as well