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Django 2.0 support, drops Django 1.10 support.
* Drops use of the, no longer maintained, django-markitup dependency in favor of django-markupfield.
* Database migrations support the conversion of all entry content and previews.
* Removes live preview in admin. See the django-markupfield project for additional usage.
* Maintains markdown support. Removes Textile support in favor of RST.
**If you previously used Textile you will have to write your own migration.** See the django-markupfield docs for assistance in this.