Nail down branch and release strategy

Once we begin supporting ES 2.0, a new plugin version must be released for each ES version. Here are some tasks and questions that need to be answered before that happens:

[ ] What will the branch names and tags look like? Should they closely follow ES, or diverge?
[ ] Does a bump in the ES patch version require a new release?
[ ] Look into https://github.com/elastic/elasticsearch-plugins-script for automating the release process
[ ] How will we react when ES releases a new version?
[ ] How do we make sure we apply bug fixes to all relevant branches?

github / elasticsearch-srv-discovery

Nail down branch and release strategy #21