Fixed typos using https://github.com/vlajos/misspell_fixer
Fixed versionchanged indentation in docs/.
Added HStoreField.

Thanks to `django-hstore` for inspiration in some areas, and many people
for reviews.
Added a warning about nonexistent FK constraints when unmigrated apps depend on migrated ones.

Thanks NotSqrt for the report; refs #23741.
Fixed links to mysqlclient in database notes.
Fixed #13181 -- Added support for callable choices to forms.ChoiceField

Thanks vanschelven and expleo for the initial patch.
Removed unused import.
Added missing docs to DiscoverRunner for keepdb option; refs #20550.
Fix minor typo in documentation.
Fixed #23531 -- Added CommonMiddleware.response_redirect_class.