Add support for Swagger.

This PR brings in swagger-express [1] which allows you to documents your APIs in your code (controllers)
Unfortunately wordnik's swagger module seems abandoned and none of the available options are particularly good.
swagger-express is the only one that I found that allows you to document your API from within the code which hopefully means
that devs can keep the API docs up-to-date more easily.

I've also updated the static swagger files to the latest release (2.0.3

[1] https://github.com/fliptoo/swagger-express