Fixed #14516 -- Extract methods from removetags and slugify template filters

Patch by @jphalip updated to apply, documentation and release notes
added.

I've documented strip_tags as well as remove_tags as the difference
between the two wouldn't be immediately obvious.

docs/releases/1.5.txt

@@ -267,6 +267,10 @@ Miscellaneous
 * :func:`~django.utils.http.int_to_base36` properly raises a :exc:`TypeError`
   instead of :exc:`ValueError` for non-integer inputs.
 
+* The ``slugify`` template filter is now available as a standard python
+  function at :func:`django.utils.text.slugify`. Similarly, ``remove_tags`` is
+  available at :func:`django.utils.html.remove_tags`.
+
 Features deprecated in 1.5
 ==========================