XSLT: Add a reference to script postprocess.js to file opml_as_xhtml.xsl;
XSLT: Add support for element category;
Python: Add support for element category.
CSS: Improve position of elements;
JS: Improve handling of content in erroneous cases;
JS: Render post as HTML when XSLT does not render correctly;
JS: Handle posts which were tagged as Text instead of HTML and vice versa;
XSLT: Adapt to be viewed on browsers with a lack of support;
XSLT: Add Support for link elements of attribute "rel";
Python: Add elements author and link of attribute "rel".
