[ACTION-331] Create xhtml example for 7 Using ITS Markup in XHTML

Hi all,

here a example file for the chapter "7. Using ITS Markup in XHTML".

I'm not sure about prefixing html elements inside the its:rules with 
"h:" like in other examples. As the default namespace is already html, i 
think this shouldn't be necessary. But Maurico told me he had problems 
with evaluating this without a prefix.

Cheers
Karl