Announce 2.1.5

* Update json-schema-core dependency to 1.1.6.
* Use msg-simple for message bundles (this addresses issue #55).
* Remove all unchecked exceptions, now unneeded.
* Improve, test all error messages.
* pom.xml improvements.
* Remove obsolete code.

Francis Galiegue (28):
      Announce 2.1.4
      Update to json-schema-core 1.1.5, lots of changes
      Update -core dependency to 1.1.6, update code accordingly
      Also update example files in javadoc
      Create the two MessageBundleProvier; modify pom.xml accordingly
      Remove ConfigurationMessageBundle, replace with a MessageBundle
      Rename JsonSchemaValidatorConfigurationBundle
      Rename, and use, the new validation bundle; delete the old one
      Remove old message resource files
      Improve error messages, part 1
      Get rid of ValidationConfigurationError
      Finish configuration error messages conversion/improvements
      Start and modify validation messages to allow parameters (#55)
      Message modifications, part 2
      TestUtils: create a static method to build a message
      TestUtils: add a comment about a possible factorization
      Reporting message improvements, part 4
      Message conversion, continued...
      Finish message conversion -- phew
      validation.properties: add crude comments
      ValidationConfigurationBuilder: fix gross error...
      Remove last unchecked, unused exception class
      Remove one unused format helper class
      JsonSchemaFactory: remove one unused variable
      Update pom.xml and dorelease.sh to reflect latest changes
      Convert README to markdown format; rename
      Add release notes file
      2.1.5