message: Update changelog.md prior to release.
diff: +## X.Y.Z (INSERT_DATE_HERE)
  +
  +#### Minor Changes
  +- [Major performance boost for CST Creation.](https://github.com/SAP/chevrotain/issues/446)
  + * **50%** speed boost measured on V8 when CST output is enabled.
  +
  +
  +
  ## 0.28.0 (4-16-2017)
  #### Major Changes
  