Update GRAMMAR-VERSIONS.md

release 0.20.0
Update CHANGELOG.md

release 0.20.0
Bump version
Update grammar versions
Bump version to proper version name
Update changelog
Merge branch 'release/0.21'
Merge tag '0.21' into develop

* Enhancements
  * [#232] Add instructions in dashboard
  * [#193] Results button properly styled
  * Finer-grain parameter-update view in dashbaord
  * [#118] Implement initial questionnaires
  * [#119] Implement final questionnaires
  * [#173] Results page fully implemented
* Bug fixes
  * [#123] Issues in questionnaire lifecycle