DEP 0201: Simplified routing syntax

[Tim Graham]

​DEP

[Tim Graham <timograham@…>]

In ee4043f:

Refs #28593 -- Moved django.conf.urls.include() to django.urls().

The old location remains for backwards compatibility. Documentation
will be updated separately along with the rest of the URL routing changes.

[Tim Graham]

The code work happened at ​PR 7482 and the documentation at ​PR 7542 and later ​PR 9072.

[Tim Graham <timograham@…>]

In df41b5a0:

Fixed #28593 -- Added a simplified URL routing syntax per DEP 0201.

Thanks Aymeric Augustin for shepherding the DEP and patch review.
Thanks Marten Kenbeek and Tim Graham for contributing to the code.
Thanks Tom Christie, Shai Berger, and Tim Graham for the docs.

[Tim Graham <timograham@…>]

In 6f7279c:

Refs #28593 -- Made URLResolver._populate() more resilient to signal interrupts.

_populate() sets the populating attribute to prevent infinite recursion in
case a urlconf includes itself. The flag is a threadlocal to avoid a race
condition [1] where one thread sets the flag and another checks it, then
proceeds to access data that's supposed to be populated (e.g. _reverse_dict)
but isn't yet.

The potential still exists for a thread to set the threadlocal, then be
interrupted by a signal such as SIGALRM and raise before resetting the
threadlocal flag. In this scenario, subsequent calls to _populate() in the
same thread will short-circuit erroneously.

The bulk of the method was already wrapped in a try/finally in df41b5a, but
since a signal interrupt can occur at any line executed by the interpreter,
this moves up the try to ensure threadlocal gets reset.

[1]: ​https://groups.google.com/d/msg/django-developers/D_bIeinKHjE/4NmVQUJqAgAJ

[Tim Graham <timograham@…>]

In f0ffa3f4:

Refs #27025, #28593 -- Fixed "invalid escape sequence" warnings in urls/resolvers.py.

[Tim Graham <timograham@…>]

In 5091bb6:

[2.0.x] Refs #27025, #28593 -- Fixed "invalid escape sequence" warnings in urls/resolvers.py.

Backport of f0ffa3f4ea277f9814285085fde20baff60fc386 from master

[Tim Graham <timograham@…>]

In 3ae9c356:

Refs #28593 -- Updated old class names in comments following URL routing changes.

[Tim Graham <timograham@…>]

In a977ae9:

[2.0.x] Refs #28593 -- Updated old class names in comments following URL routing changes.

Backport of 3ae9c356c5d4b89caf8343aa3ffe0a66e713c9fd from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7619a336:

Refs #28593 -- Changed url() to path() in comments following URL routing changes.