org-e-publish: Move publishing functions into back-end libraries
* contrib/lisp/org-e-ascii.el (org-e-ascii-publish-to-ascii,
org-e-ascii-publish-to-latin1, org-e-ascii-publish-to-utf8): New
functions.
* contrib/lisp/org-e-html.el (org-e-html-publish-to-html): New
function.
* contrib/lisp/org-e-latex.el (org-e-latex-publish-to-latex,
org-e-latex-publish-to-pdf): New functions.
* contrib/lisp/org-e-publish.el (org-e-publish-org-to-latex,
org-e-publish-org-to-pdf, org-e-publish-org-to-ascii,
org-e-publish-org-to-latin1, org-e-publish-org-to-utf8,
org-e-publish-org-to-html): Remove functions.
Each back-end can define its own publishing functions. This patch
avoids to clutter org-e-publish.el.