docs: use ‘stable’ tag in Django URLs

In URLs that point to pages in django
documentation, use 'stable' tag in order to
always point to the latest version of the documentation.
Previously, hard-coded django versions (e.g. 1.7)
were used which are now outdated (throw 404) e.g. this link:
https://docs.djangoproject.com/en/1.7/topics/class-based-views/
is no longer valid used in `views_and_forms.html`
page.

Using 'stable' tag will ensure those
links never become outdated.

docs: work around ReST pedantry !cosmetic

Bump version to 2.5.dev2


new: SearchQuerySet.set_spelling_query for custom spellcheck

This makes it much easier to customize the text sent to the
backend search engine for spelling suggestions independently
from the actual query being executed.

v2.3.2 maintenance update

Release 2.4.0

v2.4.0 release candidate

Bump version to 2.4.0.dev1