Allow for adding pathelements to hst:link tag

Sometimes request parameters are added to a url in the form of path elements of the url. This is the so called "clean url" method. Example: www.cars.com/model/mymodel/color/red/.
To support this way of working hst should allow for a <hst:pathelement value="model" /> that can be nested in hst:link, hst:renderurl and hst:actionurl tags. Just like the <hst:param/> tag.

It should be possible to combine both tags. Logical way of processing would be to add the hst:pathelement tags first, in the order given, and then the hst:param tags in the order given.