Use chaining/mixins provided by `express-context` v0.5.0.

This allows for a more "fire and forget" approach to including authentication middleware. No longer do you need to use several use statements just to eke out one `auth.required()`. Everything will automatically be included for you now. Some thought needs to go into ensuring things don't get processed twice now, however.
Merge pull request #3 from izaakschroeder/chaining

Use chaining/mixins provided by `express-context` v0.5.0.