Update documentation related to the sitemaps

Since we now use regular Django sitemaps we can mostly just refer to the
Django documentation

Co-authored with @mikedingjan

docs/reference/contrib/sitemaps.rst

@@ -3,24 +3,42 @@
 Sitemap generator
 =================
 
-This document describes how to create XML sitemaps for your Wagtail website using the ``wagtail.contrib.wagtailsitemaps`` module.
+This document describes how to create XML sitemaps for your Wagtail website
+using the ``wagtail.contrib.wagtailsitemaps`` module.
+
+
+.. note::
+
+    As of Wagtail 1.10 the Django contrib sitemap app is used to generate
+    sitemaps.  However since Wagtail requires the Site instance to be available
+    during the sitemap generation you will have to use the views from the
+    ``wagtail.contrib.wagtailsitemaps.views`` module instead of the views
+    provided by Django (``django.contrib.sitemaps.views``). 
+    
+    The usage of these views is otherwise identical, which means that
+    customisation and caching of the sitemaps are done using the default Django
+    patterns.  See for in-depth information the Django documentation. 
 
 
 Basic configuration
 ~~~~~~~~~~~~~~~~~~~
 
-You firstly need to add ``"wagtail.contrib.wagtailsitemaps"`` to INSTALLED_APPS in your Django settings file:
+
+You firstly need to add ``"django.contrib.sitemaps"`` to INSTALLED_APPS in your
+Django settings file:
 
  .. code-block:: python
 
     INSTALLED_APPS = [
         ...
 
-        "wagtail.contrib.wagtailsitemaps",
+        "django.contrib.sitemaps",
     ]
 
 
-Then, in ``urls.py``, you need to add a link to the ``wagtail.contrib.wagtailsitemaps.views.sitemap`` view which generates the sitemap:
+Then, in ``urls.py``, you need to add a link to the
+``wagtail.contrib.wagtailsitemaps.views.sitemap`` view which generates the
+sitemap:
 
 .. code-block:: python
 
@@ -38,14 +56,17 @@ Then, in ``urls.py``, you need to add a link to the ``wagtail.contrib.wagtailsit
     ]
 
 
-You should now be able to browse to ``/sitemap.xml`` and see the sitemap working. By default, all published pages in your website will be added to the site map.
+You should now be able to browse to ``/sitemap.xml`` and see the sitemap
+working. By default, all published pages in your website will be added to the
+site map.
 
 
 Setting the hostname
 ~~~~~~~~~~~~~~~~~~~~
 
-By default, the sitemap uses the hostname defined in the Wagtail Admin's ``Sites`` area. If your
-default site is called ``localhost``, then URLs in the sitemap will look like:
+By default, the sitemap uses the hostname defined in the Wagtail Admin's
+``Sites`` area. If your default site is called ``localhost``, then URLs in the
+sitemap will look like:
 
  .. code-block:: xml
 
@@ -55,8 +76,9 @@ default site is called ``localhost``, then URLs in the sitemap will look like:
     </url>
 
 
-For tools like Google Search Tools to properly index your site, you need to set a valid, crawlable hostname. If you change the site's hostname from ``localhost`` to ``mysite.com``, ``sitemap.xml``
-will contain the correct URLs:
+For tools like Google Search Tools to properly index your site, you need to set
+a valid, crawlable hostname. If you change the site's hostname from
+``localhost`` to ``mysite.com``, ``sitemap.xml`` will contain the correct URLs:
 
  .. code-block:: xml
 
@@ -75,7 +97,10 @@ Customising
 URLs
 ----
 
-The ``Page`` class defines a ``get_sitemap_urls`` method which you can override to customise sitemaps per ``Page`` instance. This method must return a list of dictionaries, one dictionary per URL entry in the sitemap. You can exclude pages from the sitemap by returning an empty list.
+The ``Page`` class defines a ``get_sitemap_urls`` method which you can override
+to customise sitemaps per ``Page`` instance. This method must return a list of
+dictionaries, one dictionary per URL entry in the sitemap. You can exclude
+pages from the sitemap by returning an empty list.
 
 Each dictionary can contain the following:
 
@@ -84,10 +109,14 @@ Each dictionary can contain the following:
  - **changefreq**
  - **priority**
 
-You can add more but you will need to override the ``wagtailsitemaps/sitemap.xml`` template in order for them to be displayed in the sitemap.
+You can add more but you will need to override the
+``sitemap.xml`` template in order for them to be displayed in the sitemap.
 
 
-Cache
------
+Serving multiple sitemaps
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
-By default, sitemaps are cached for 100 minutes. You can change this by setting ``WAGTAILSITEMAPS_CACHE_TIMEOUT`` in your Django settings to the number of seconds you would like the cache to last for.
+If you want to support the sitemap indexes from Django then you will need to
+use the index view from ``wagtail.contrib.sitemaps.views`` instead of the
+index view from ``django.contrib.sitemaps.views``.  Please see for further
+details the Django documentation.

wagtail/contrib/wagtailsitemaps/tests.py

@@ -1,7 +1,6 @@
 from __future__ import absolute_import, unicode_literals
 
 from django.contrib.sites.shortcuts import get_current_site
-from django.core.cache import cache
 from django.test import RequestFactory, TestCase
 
 from wagtail.tests.testapp.models import EventIndex, SimplePage