Gradle: use release flag instead of sourceCompatibility and targetCom…

…patibility.

Fixes FlatBufferBuilder using ByteBuffer instead of Buffer API.

Publish: set signing config after publication is known.

Prepare release 2.9.0

Prepare release 0.8.1

README.md: typos

2.7.1 release

change versions to 2.7.0 (release)

Prepare version 2.6.0.

Prepare version 2.6.0-RC.

Prepare version 3.0.0-alpha2.