refactored documentation

doc/filters/capitalize.rst

@@ -0,0 +1,11 @@
+``capitalize``
+==============
+
+The ``capitalize`` filter capitalizes a value. The first character will be
+uppercase, all others lowercase:
+
+.. code-block:: jinja
+
+    {{ 'my first car'|capitalize }}
+
+    {# outputs 'My first car' #}