[O] New html exporter and filters

[Rick Frankel]

This may be a question for Nicolas ---

I seem to have reached the limit of my emacs-fu. I am looking at
adding XOXO output to the S5 exporter (S5 has built-in support for
XOXO structured documents) and was trying to use an element (headline)
filter to modify the document structure. I am also trying to change
the div id to make them more friendly to the deck.js goto function
(which accumulates and displays the ids as a menu).

When i look at the `contents' passed to the filter in edebug, i can see
the element properties (level, raw-title, etc) in the output but I
cannot figure out how to access them.

On the other hand, it would be easier if ox-html were modified so that
org-html-headline uses a variable (or callback) for the format of the
wrapper (currently "<div id=\"%s...") and a callback for the div id
generation. This would add flexibility for inherited backends as well
as allow for more "html5ish" structures (e.g., <section> and <article>
instead of generic <divs>).

The structure of the new exporter has made if very easy for me to add
new html based exporters using the derived backends. Minor changes to
ox-html would make this even more flexible.

I am willing make the changes to ox-html if the approach is agreeable.

tia,
rick