org-trec-export:
	* add (unimplemented) org-trec-escape wrapper for all strings
	* add actual link in link output (e.g. [[alink][a]] -> a <alink>)
    	* create template function to actually wrap results in TREC XML
    	  block
org-trec-export:
	* implement proper XML escaping
	* include filename
	* include HTML header tags on headlines