GitHub release notes

[by-dam]

Use the ReleaseNotesPlugin to publish the version on Github.

It uses the Github API in a similar way as the Jira API and creates a release as described here: https://developer.github.com/v3/repos/releases/#create-a-release

The Github auth token must be provided as in the env variable: GITHUB_AUTH_TOKEN

Note: Includes https://github.com/cakesolutions/sbt-cake/pull/65