[DO NOT MERGE YET] XD-925: REST Documentation

Simple POC showing usage of https://github.com/wordnik/swagger-core

Build and browse to http://localhost:9393/swagger

Note that this uses an old version of Swagger/Spring integration (0.6.4 in maven central, while current version is 0.7.0-SNAPSHOT)

If we don't want the UI, there's also the option of exploiting the exposed metadata to e.g. generate asciidoc.

Also note that this is the result with absolutely customization (no extra annotations on controllers, etc)