Fixed docs for setting up with express

In connect-sequelize.js:20 the passed argument is used as:

module.exports = function SequelizeSessionInit(express) {
    var Store = express.Store || express.session.Store;
...
}
Merge branch 'findOrCreate-fix' of https://github.com/shadone/connect-sequelize
bump merge fix.
Added a callback option to SequelizeStore.

There should be a way to know when the "Sessions" model was synchronized with
the database to avoid race condition on server startup.