Support publishing of multiple versions of docs

[spencergibb]

This url is master http://projects.spring.io/spring-cloud/spring-cloud.html but looks like the current version. It should have a snapshot url.

See http://projects.spring.io/spring-boot/ for what it should look like.

[spencergibb]

Looks like this is it: https://github.com/olivergierke/spring-data-release-cli

[dsyer]

We have multiple versions of docs in the cloud.spring.io/static site (spring-cloud/spring-cloud-static).