Implement MutableMapping in DocumentMetaWrapper
Implement MutableMapping in DocumentMetaWrapper

Meta is optional (for EmbeddedDocuments) in MongoEngine 0.7.x and requires more
of dict's raw functionality.

carlware/django-mongodbforms,thomwiggers/django-mongodbforms,fmoro/django-mongodbforms,lucidbard/django-mongodbforms,jschrewe/django-mongodbforms