Adapt the xml plugin/consider creating new plugin for handling proper html files

[astefan]

A html file does resemble (to a certain degree) to an xml file.
The current xml filter plugin fails to parse anything that involves a tag that doesn't have a closing end (for example the <br> tag), but otherwise it should work just fine with an xml-like html file.

[jordansissel]

+1 on the feature. I think maybe we could make a new filter 'html' to do this, unless we have a good story about why the filter called 'xml' should also handle html.