Added support for dx and dy properties for text. A bit of plumbing was already in place so I completed that.
http://www.w3.org/TR/SVG11/text.html#TextElementDXAttribute
http://www.w3.org/TR/SVG11/text.html#TextElementDYAttribute
Merge pull request #62 from tobiasoort/master

Added support for dx and dy properties for text.