Add markdown in long-description for xml-based templates

[siad007]

Fixes #1064

[mvriel]

I am sorry but this approach does not fit with the strategy for the XML output.

The XML output should not contain HTML markup as we might need to move to different output formats in the future. Transforming a text from markdown to html should be done in the template itself (as the twig renderer has a markdown filter).

What can be done is use a php function in XSL to transform from the markdown text to html as is shown in this article: http://techportal.inviqa.com/2009/12/16/transforming-xml-with-php-and-xsl/ (look for the chapter Calling PHP functions from XSLT); this way it is possible to add filters to XSL

[siad007]

ah ok i get that point