doc_layout : added class DocListElementFull, DocListElementSpan and DocListElementLink

DocListElementFull : generate a list of element with optional spans and links
<li class='something'><span title='something'>I||H||R</span><a href='something' title='something'>module_name<a></li>

DocListElementSpan : generate a span for a DocListElementFull :
<span title='something'>I||H||R</span>

DocListElementLink : generate a link for a DocListElementFull :
<a href='something' title='something'>module_name<a>

modified DocSidebox for beeing able to modify the css class of the nav tag

Signed-off-by: Maxime Leroy <maxime.leroy76@gmail.com>
nitdoc : use doc_layout for sidebar html generation on a module page

added : method html_short_comment in MClass class
added : method html_short_comment in MModule class
fixed : class NitdocOverview for using the new DocListElementFull in doc_layout


Signed-off-by: Maxime Leroy <maxime.leroy76@gmail.com>