Fixed #15233 -- reST/Sphinx markup corrections in numerous areas, mostly...

Fixed #15233 -- reST/Sphinx markup corrections in numerous areas, mostly centering around bad crossref targets. Thanks to Aryeh Leib Taurog for the draft patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15549 bcc190cf-cafb-0310-a4f2-bffc1f526a37