Add support for Express 4.x

Added support for Express 4.x by allowing direct reference to `session` to be passed into connect-mongostore since session is no longer bundled with Express. It is still backward compatible with Connect and Express 3.x. With this change, I bumped to version to 0.1.0 since this is a backwards compatible API change. I've also added a `History.md` file to track changes going forward.

If you have any questions on the changes, please free to let me know.