Complete release note file

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
project.gradle: add a javadoc link

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
IDEA inspection run

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
2.1.7

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Announce 2.1.7

* Import all format attributes from
  [json-schema-formats](https://github.com/fge/json-schema-formats).
* Switch to gradle for build.
* Major dependencies updates; drop ServiceLoader for message bundles.
* Fix javadoc generation.

Francis Galiegue (16):
      Announce 2.1.6
      Switch to gradle; update dependencies, update code
      README updates
      Import format attributes from json-schema-formats
      Start to add test for extra format attributes, starting with "base64"
      Add test for the sha1 format attribute
      Move HexStringFormatAttribute to the helpers package
      dorelease.sh: use Gradle
      Update release notes
      New file CONTRIBUTORS.md
      Fix javadoc generation
      Add a comment about javadoc mishaps
      Complete release note file
      project.gradle: add a javadoc link
      IDEA inspection run
      2.1.7

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>