doc: Moved Jinja links to new home page and HTTPS

Seems like Jinja is no longer pocoo project but
palletsprojects.com

doc/templating.rst

@@ -6,10 +6,11 @@
 Templating
 ==========
 
-Sphinx uses the `Jinja <http://jinja.pocoo.org>`_ templating engine for its HTML
-templates.  Jinja is a text-based engine, inspired by Django templates, so
-anyone having used Django will already be familiar with it.  It also has
-excellent documentation for those who need to make themselves familiar with it.
+Sphinx uses the `Jinja <https://jinja.palletsprojects.com/>`_ templating engine
+for its HTML templates.  Jinja is a text-based engine, inspired by Django
+templates, so anyone having used Django will already be familiar with it. It
+also has excellent documentation for those who need to make themselves familiar
+with it.
 
 
 Do I need to use Sphinx's templates to produce HTML?

doc/usage/advanced/websupport/quickstart.rst

@@ -61,7 +61,7 @@ This will return a dictionary containing the following items:
 
 This dict can then be used as context for templates.  The goal is to be easy to
 integrate with your existing templating system.  An example using `Jinja2
-<http://jinja.pocoo.org/>`_ is:
+<https://jinja.palletsprojects.com/>`_ is:
 
 .. code-block:: html+jinja
 

doc/usage/extensions/autosummary.rst

@@ -335,4 +335,4 @@ the title of a page.
    You can use the :rst:dir:`autosummary` directive in the stub pages.
    Stub pages are generated also based on these directives.
 
-.. _`escape filter`: http://jinja.pocoo.org/docs/2.9/templates/#escape
+.. _`escape filter`: https://jinja.palletsprojects.com/en/3.0.x/templates/#jinja-filters.escape

doc/usage/theming.rst

@@ -248,7 +248,7 @@ These themes are:
 
 **scrolls**
   A more lightweight theme, based on `the Jinja documentation
-  <http://jinja.pocoo.org/>`_.  The following color options are available:
+  <https://jinja.palletsprojects.com/>`_.  The following color options are available:
 
   - **headerbordercolor**
   - **subheadlinecolor**