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Release date: 2018/5/29
- Add basic unit test.
- Update resources, fix plugin register bug, use CKEditor 4.9.2.
- Add configuration parameter ``CKEDITOR_ENABLE_CODESNIPPET``, used to
enable/disable ``Code Snippet`` plugin.
- Added Markdown plugin into built-in resouce, enabled markdown mode
via ``CKEDITOR_ENABLE_MARKDOWN``.
- Added configuration parameter ``CKEDITOR_EXTRA_PLUGINS``, a list used
to register extra plugins.