Release 2.1.6

Prepare release 2.1.5

Prepare 2.1.4 release

2.1.3 release preparation (#825)

[maven-release-plugin] copy for tag 2.1.2

[maven-release-plugin] copy for tag 2.1.1

[maven-release-plugin] copy for tag 2.1.0

[maven-release-plugin] copy for tag 2.1.0-beta.12

[maven-release-plugin] copy for tag 2.1.0-beta.11

[maven-release-plugin] copy for tag 2.1.0-beta.10