SF bug 1046690:  difflib.HtmlDiff doc errors.
SF bug 1046690:  difflib.HtmlDiff doc errors.

Easy doc corrections from Dan Gass.
Also repaired the LaTeX for optional keyword arguments throughout, which
was (incorrectly) nested instead of flat.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator