Create sequelize object from json file.

This provides a wrapper around the Sequelize constructor to instantiate a new sequelize object from a json configuration file. You can pass in the path and env as options.

This is handy if you use migrations, and you want to share the configuration settings that the migration binary creates. 

I've been using this in my own project, but this is more to start a discussion. I'm not sure if this is in line with design goals or plans.