Rework vsbase.XmlFormatter to be easier to customize.
Rework vsbase.XmlFormatter to be easier to customize.

Organize code in a way that makes it easy to customize output XML
formatting by overwriting some simple methods. The interface is flexible
enough to accommodate even such weird formattings as those used by
VS200x.

vslavik/bakefile,vslavik/bakefile,vslavik/bakefile