added missing docs

doc/filters/data_uri.rst

@@ -0,0 +1,44 @@
+``data_uri``
+============
+
+.. versionadded:: 2.12
+    The ``data_uri`` filter was added in Twig 2.12.
+
+The ``data_uri`` filter generates a URL using the data scheme as defined in RFC
+2397:
+
+.. code-block:: twig
+
+    {{ image_data|data_uri }}
+
+    {{ source('path_to_image')|data_uri }}
+
+    {# force the mime type, disable the guessing of the mime type #}
+    {{ image_data|data_uri(mime="image/svg") }}
+
+    {# also works with plain text #}
+    {{ '<b>foobar</b>'|data_uri(mime="text/html") }}
+
+    {# add some extra parameters #}
+    {{ '<b>foobar</b>'|data_uri(mime="text/html", parameters={charset: "ascii"}) }}
+
+.. note::
+
+    The ``data_uri`` filter is part of the ``HtmlExtension`` which is not
+    enabled by default; you must add it explicitly on the Twig environment::
+
+        use Twig\Extension\HtmlExtension;
+
+        $twig = new \Twig\Environment(...);
+        $twig->addExtension(new HtmlExtension());
+
+.. note::
+
+    The filter does not perform any length validation on purpose (limits depends
+    on the usage context), validation should be done before calling this filter.
+
+Arguments
+---------
+
+* ``mime``: The mime type
+* ``parameters``: An array of parameters

doc/filters/index.rst

@@ -9,6 +9,7 @@ Filters
     capitalize
     column
     convert_encoding
+    data_uri
     date
     date_modify
     default