Add documentation page for number_format.

doc/filters/index.rst

@@ -7,6 +7,7 @@ Filters
     date
     format
     replace
+    number_format
     url_encode
     json_encode
     convert_encoding

doc/filters/number_format.rst

@@ -0,0 +1,39 @@
+``number_format``
+=================
+
+.. versionadded:: 1.6
+    The number_format filter was added in Twig 1.6
+
+The ``number_format`` filter formats numbers.  It is a wrapper around PHP's
+`number_format`_ function:
+
+.. code-block:: jinja
+
+    {{ 200.35|number_format }}
+
+You can control the number of decimal places, decimal point, and thousands
+separator using the additional arguments:
+
+.. code-block:: jinja
+
+    {{ 9800.333|number_format(2, ',', '.') }}
+
+If no formatting options are provided then Twig will use the default formatting
+options of:
+
+- 0 decimal places.
+- ``.`` as the decimal point.
+- ``,`` as the thousands separator.
+
+These defaults can be easily changed through the core extension:
+
+.. code-block:: php
+
+    $twig = new Twig_Environment($loader);
+    $twig->getExtension('core')->setNumberFormat(3, ',', '.');
+
+The defaults set for ``number_format`` can be over-ridden upon each call using the
+additional parameters.
+
+.. _`number_format`: http://php.net/number_format
+