Fixed #21747 -- Added {% elif %} to template topics guide.

Thanks gcc for the suggestion.
Fixed #21727 -- Added some links to help clarify topics/auth/default.txt

Thanks daGrevis for the suggestion.
Fixed #21768 -- Corrected TemplateView context section.

Thanks nedbatchelder for the report and claudep for the patch.
Fixed #21343 -- Noted many-to-many restrictions with intermediate model.

Thanks EvilDMP for the report.
Fixed #21740 -- Stopped using mutable default arguments in test client

Thanks Denver Coneybeare for the report and initial patch, and
Atala for another patch.
Fixed #21784: Correctly decode stdin input for migration defaults
Fixed typo in docstring.
Merge pull request #2176 from numerodix/master

Fixed typo in docstring.