[2.0.x] Refs #28643 -- Reorganized database functions docs.

Thanks Tim Graham for the review.

Backport of ad8036d7 from master

docs/releases/1.10.txt

@@ -423,12 +423,12 @@ Models
 * A proxy model may now inherit multiple proxy models that share a common
   non-abstract parent class.
 
-* Added :class:`~django.db.models.functions.datetime.Extract` functions
-  to extract datetime components as integers, such as year and hour.
+* Added :class:`~django.db.models.functions.Extract` functions to extract
+  datetime components as integers, such as year and hour.
 
-* Added :class:`~django.db.models.functions.datetime.Trunc` functions to
-  truncate a date or datetime to a significant component. They enable queries
-  like sales-per-day or sales-per-hour.
+* Added :class:`~django.db.models.functions.Trunc` functions to truncate a date
+  or datetime to a significant component. They enable queries like
+  sales-per-day or sales-per-hour.
 
 * ``Model.__init__()`` now sets values of virtual fields from its keyword
   arguments.
@@ -894,8 +894,8 @@ Miscellaneous
   yourself.
 
 * Private expressions ``django.db.models.expressions.Date`` and ``DateTime``
-  are removed. The new :class:`~django.db.models.functions.datetime.Trunc`
-  expressions provide the same functionality.
+  are removed. The new :class:`~django.db.models.functions.Trunc` expressions
+  provide the same functionality.
 
 * The ``_base_manager`` and ``_default_manager`` attributes are removed from
   model instances. They remain accessible on the model class.

docs/releases/1.11.txt

@@ -330,16 +330,16 @@ Models
   (This validator moved to the form field in :doc:`Django 1.11.2 <1.11.2>`.)
 
 * Added support for time truncation to
-  :class:`~django.db.models.functions.datetime.Trunc` functions.
+  :class:`~django.db.models.functions.Trunc` functions.
 
-* Added the :class:`~django.db.models.functions.datetime.ExtractWeek` function
-  to extract the week from :class:`~django.db.models.DateField` and
+* Added the :class:`~django.db.models.functions.ExtractWeek` function to
+  extract the week from :class:`~django.db.models.DateField` and
   :class:`~django.db.models.DateTimeField` and exposed it through the
   :lookup:`week` lookup.
 
-* Added the :class:`~django.db.models.functions.datetime.TruncTime` function
-  to truncate :class:`~django.db.models.DateTimeField` to its time component
-  and exposed it through the :lookup:`time` lookup.
+* Added the :class:`~django.db.models.functions.TruncTime` function to truncate
+  :class:`~django.db.models.DateTimeField` to its time component and exposed it
+  through the :lookup:`time` lookup.
 
 * Added support for expressions in :meth:`.QuerySet.values` and
   :meth:`~.QuerySet.values_list`.

docs/releases/2.0.txt

@@ -245,20 +245,20 @@ Models
   :attr:`Meta.get_latest_by <django.db.models.Options.get_latest_by>`  now
   allow ordering by several fields.
 
-* Added the :class:`~django.db.models.functions.datetime.ExtractQuarter`
-  function to extract the quarter from :class:`~django.db.models.DateField` and
+* Added the :class:`~django.db.models.functions.ExtractQuarter` function to
+  extract the quarter from :class:`~django.db.models.DateField` and
   :class:`~django.db.models.DateTimeField`, and exposed it through the
   :lookup:`quarter` lookup.
 
-* Added the :class:`~django.db.models.functions.datetime.TruncQuarter`
-  function to truncate :class:`~django.db.models.DateField` and
+* Added the :class:`~django.db.models.functions.TruncQuarter` function to
+  truncate :class:`~django.db.models.DateField` and
   :class:`~django.db.models.DateTimeField` to the first day of a quarter.
 
 * Added the :attr:`~django.db.models.Index.db_tablespace` parameter to
   class-based indexes.
 
 * If the database supports a native duration field (Oracle and PostgreSQL),
-  :class:`~django.db.models.functions.datetime.Extract` now works with
+  :class:`~django.db.models.functions.Extract` now works with
   :class:`~django.db.models.DurationField`.
 
 * Added the ``of`` argument to :meth:`.QuerySet.select_for_update()`, supported