improve xqdoc documentation

[Sorin Marian Nasoi]

We should have a method similar to the \include option provided by doxygen
in order to include files/tests into the xqdoc documentation.

Details:
- in Doxygen if you made sure that in the doc/zorba/doxy.config.in you set the:
EXAMPLE_PATH at line 501 and EXAMPLE_PATTERNS at line 510 in the doxy
documentation you could use

\include file.xml and get the content of the file.xml

the result of the XHTML code was a DIV and PRE containers that were
added to the actual code in the file, see for example
http://www.zorba-xquery.com/doc/zorba-latest/zorba/html/converters.html
the test shown after the text "The following XQuery (taken from John
Snelson's article mentioned above) demonstrates the usage of the parse
function."

There you see that <div class="fragment"><pre class="fragment"> are
added before the content of the actual file \included. Off course
class="fragment" should be implemented in the CSS, but that is besides
the point.

A simpler solution, for starters would be to add some links like this:
<a href="file:///file.xml" target="_blank">file.xml</a> and then you
put the file.xml in a path recognized by xqdoc (I think the same thing
is done the links to the actual modules pages, in xhtml/index.html,
right?)
In this case I think the question is in which folder should we store the file.xml.

[Sorin Marian Nasoi (sorin.marian.nasoi)]

We already have this in Zorba.