Rally release 1.4.0

Rally release 1.3.0

Rally release 1.2.1

Document which ES versions are supported by Rally

With this commit we add a dedicated page to our documentation that
explains which Elasticsearch versions can be benchmarked with which
Rally version. As our documentation is versioned, this helps users to
determine whether their version of Rally can benchmark a specific
Elasticsearch version.

Relates elastic#714

Rally release 1.1.0

Rally release 1.0.4

Rally release 1.0.3

Rally release 1.0.2

Rally release 1.0.1

Rally release 1.0.0