ox-ascii/ox-latex/ox-html: Make use of optional title in toc
* lisp/ox-ascii.el (org-ascii--build-title): Add an argument. Use
optional title when building a toc line.
(org-ascii--build-toc): Call `org-ascii--build-title' with appropriate
arguments.
* lisp/ox-latex.el (org-latex-headline): Use optional title for table
of contents.
* lisp/ox-html.el (org-html--toc-text): Renamed from
`org-html-toc-text'. Add docstring.
(org-html--format-toc-headline): Renamed from
`org-html-format-toc-headline'. Add docstring. Use optional title if
possible.
(org-html-toc): Add docstring.