message: CHORE: update changelog for release.
diff: +## X.Y.Z (INSERT_DATE_HERE)
  +
  +#### Breaking Changes
  +- [DSL Methods Improved optional arguments syntax.](https://github.com/SAP/chevrotain/issues/367)
  +
  +#### Major Changes
  +- [Automatic creation of a Concrete Syntax Tree.](https://github.com/SAP/chevrotain/issues/215)
  + * See [Relevant Docs]( https://github.com/SAP/chevrotain/blob/master/docs/concrete_syntax_tree.md).
  +
  +#### Minor Changes
  +- [Clear error message if rules have been defined after performSelfAnalysis has been called.](https://github.com/SAP/chevrotain/issues/385)
  +- [Micro performance boost on subrule array init.](https://github.com/SAP/chevrotain/issues/378)
  +
  +#### Bug Fixes
  +- [Avoid Possible internal unique key conflicts.](https://github.com/SAP/chevrotain/commit/393f2a97cd109c239ced67931586afe5034df713)
  +- [Infinite loop during GAST builder.](https://github.com/SAP/chevrotain/issues/392)
  +
  +
  +
  ## 0.23.0 (2-3-2017)
  #### Major Changes
  