[#1894] Update docs and example_idatasetform to reflect changes

I kept the example of removing the default key/value extras, as this is
what most people would want to do anyway, but mentioning that you have
the option of combining them both on CKAN >= 2.2.1

ckanext/example_idatasetform/templates/package/snippets/package_metadata_fields.html

@@ -1,9 +1,7 @@
 {% ckan_extends %}
 
-{# Remove 'free extras' from the package form. If you're using
-convert_to/from_extras() as we are with our 'custom_text' field below then
-you need to remove free extras from the form, or editing your custom field
-won't work. #}
+{# Remove 'free extras' from the package form, as we don't want to support
+   them on our example. #}
 {% block custom_fields %}
 {% endblock %}
 

doc/extensions/adding-custom-fields.rst

@@ -144,7 +144,8 @@ the templates. Create a directory called
 ``ckanext-extrafields/ckanext/extrafields/templates/package/snippets/``.
 
 We need to override a few templates in order to get our custom field rendered.
-Firstly we need to remove the default custom field handling. Create a template
+A common option when using a custom schema is to remove the default custom
+field handling that allows arbitrary key/value pairs. Create a template
 file in our templates directory called 
 ``package/snippets/package_metadata_fields.html`` containing
 
@@ -154,7 +155,16 @@ file in our templates directory called
     :end-before: {% block package_metadata_fields %}
 
 This overrides the custom_fields block with an empty block so the default CKAN
-custom fields form does not render. Next add a template in our template 
+custom fields form does not render.
+
+
+.. versionadded:: 2.2.1
+
+    Starting from CKAN 2.2.1 you can combine free extras with custom fields
+    handled with ``convert_to_extras`` and ``convert_from_extras``. On prior
+    versions you'll always need to remove the free extras handling.
+
+Next add a template in our template
 directory called ``package/snippets/package_basic_fields.html`` containing
 
 .. literalinclude:: ../../ckanext/example_idatasetform/templates/package/snippets/package_basic_fields.html