Merge pull request #1370 from Matt-Stevens/doc-url-fix

Fixed broken Atom URLs in syndication docs
Fixed #20762 -- Clarified that add_fieldsets is not a standard ModelAdmin attribute.
Cleaned up UserAdmin.get_form() that worked around a bug fixed in 23e1b59.

Refs #18681.
Merge pull request #1372 from loic/admin

Cleaned up UserAdmin.get_form() that worked around a bug fixed in 23e1b59.
Fixed #20767 -- Fixed ModelAdmin.preserve_filters for namespaced URLs.

Thanks Collin Anderson for the report.
LocaleMiddleware isn't default anymore

Changed in @23229061fcb836ecca2195cc75f91e331279a5d1
Fix Croatia's country code in `localflavor` docs

Croatia's country code is 'HR', not 'CR'.
Updated the `databases` documentation

 + Removed a reference about MySQL storage engines also being
   called 'table types', as this term has been deprecated for
   8 years and is no longer used.

 + Fixed the link to the official InnoDB storage engine docs.

 + Apache (versions >= 2.4) will always choose a multi-threaded
   MPM module on modern operating systems (later than 2002).
Fixed #20772 -- Fixed minor typo in form media docs.
Merge pull request #1378 from loic/docs

Fixed #20772 -- Fixed minor typo in form media docs.
Merge pull request #1375 from Matt-Stevens/master

Fixed Croatia's country code in `localflavor` docs
Merge pull request #1377 from Matt-Stevens/doc-fixes-ref-databases

Updated the `databases` documentation
Merge pull request #1374 from seocam/fix_i18n_docs

LocaleMiddleware isn't default anymore (corrected docs)
Fixed #14656 -- Added Atom1Feed `published` element

Some feed aggregators make use of the `published` element as well as
the `updated` element (within the Atom standard -- http://bit.ly/2YySb).

The standard allows for these two elements to be present in the same
entry. `Atom1Feed` had implemented the `updated` element which was
incorrectly taking the date from `pubdate`.
Fixed #18551 -- Enabled skipIfDBFeature/skipUnlessDBFeature to decorate a class

Thanks Tim Graham for the review and improved patch.
Fixed #20765 -- Set small values of `step` using exponential notation.

Browsers parse small factors of 10 as 0 under decimal notation.

Thanks to Trac alias matklad for the report and Claude Paroz for the review.
Fixed #13696 -- ensured inline pk field is rendered
Fixed an email validation regression

Thanks Vincent Wagelaar for the report.
Fixed #13629 -- Added CSS classes to the `<body>` tag of some admin templates to allow style customizations per app or per model.
Fixed #20781 -- Fixed _has_changed regression with MultiValueField

Thanks Tim Graham for the report.