org-e-html: New HTML exporter - a first attempt

* contrib/lisp/org-export.el (org-export-dispatch)
(org-export-dispatch-ui): Add new entries for the new HTML
exporter.

* EXPERIMENTAL/org-e-html.el: New file.  This is a very rough
cut based out on org-xhtml.el and org-e-latex.el.  The file
retains all the LaTeXisms in either commented form or
otherwise.  This is deliberate so as to have a quick look at
the reference implementation.  Retaining the organization
style of org-xhtml.el would enable easy creation of
org-e-odt.el by simply replacing e-html with e-odt for the
most part.
The changes here covers fairly a good ground - say 90% - of my
unit test file.

contrib/lisp/org-export.el

@@ -3211,6 +3211,14 @@ Return an error if key pressed has no associated command."
       (?d (org-open-file
 	   (org-e-latex-export-to-pdf
 	    (memq 'subtree optns) (memq 'visible optns) (memq 'body optns))))
+
+      ;; Export with `e-html' back-end.
+      (?h (org-e-html-export-to-html
+	   (memq 'subtree optns) (memq 'visible optns) (memq 'body optns)))
+      (?b (org-open-file
+      	   (org-e-html-export-to-html
+      	    (memq 'subtree optns) (memq 'visible optns) (memq 'body optns))))
+
       ;; Publishing facilities
       (?F (org-e-publish-current-file (memq 'force optns)))
       (?P (org-e-publish-current-project (memq 'force optns)))
@@ -3254,6 +3262,9 @@ final interactive export options as CDR."
 \[l] to TEX file               [L] to temporary buffer
 \[p] to PDF file               [d] ... and open it
 
+---------------------  HTML Export  -----------------------
+\[h] to HTML file              [b] ... and open it
+
 ------------------------- Publish -------------------------
 \[F] current file              [P] current project
 \[X] a project                 [E] every project"