Use native geometry types on PostGIS 2.0+ instead of `AddGeometryColumn` and don't query database in `PostGISCreation.sql_table_creation_suffix`.

Reorganized topic document so it introduces concepts form simple to more
complex. Moved reference parts to their own documents.

This is easier to track changes through the VCS.

This is especially needed to compare XML when hash randomization
is on, as attribute order may vary. Refs #17758, #19038.
Thanks Taylor Mitchell for the initial patch, and Ian Clelland for
review and cleanup.

Thanks to Preston Holmes for the suggestion.

Thanks to Bradley Ayers for the review.

Thanks to Ivan Virabyan for the report and initial patch.

Fixed `F()` expression regressions in GeoDjango caused by recent datastructure changes in `SQLEvaluator`.

Thanks Flavio Curella for the report and the initial patch.

Fixed typo in queryset docs under update method.

Fixed #18413 - Noted that a model's files are not deleted when the model is deleted. Thanks lawgon for the report.

Previously, a duplicate model, codename for permission would lead to
database integrity error. Cleaned the implementation so that this case
now raises an CommandError instead.

Thanks lmisek@go2.pl for the report.

Thanks Paolo Corti for the suggestion.

Thanks to Ivan Virabyan for the report.

thanks @freakboy3742 for the catch and review