doc: Moved Jinja links to new home page and HTTPS

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

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**