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Overhaul of the Ybe data structure, moved away from ``text_markup`` and ``text_html`` and instead
use Yaml tags for this purpose. In the new system, marking a text item as markdown is now done using ``field: !markdown text...``.
Additionally, this version supports question comments with QTI reading and writing support.
Added
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- Adds QTI writing support for hints and explanations.
Changed
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- Updated the Ybe format. Adds hints and explanations as fields.