title: pySVG css links
body: <p>I'm trying to figure out pySVG, having trouble understanding how to link to an external CSS file, does pySVG handle this?  Looking over the documentation, the style seems to be hard coded in most of the examples. </p>
  
  <p>Further, I'd love to add an 'onclick' to change the CSS reference, so, a heat map (for example) could link to a default CSS which styles elements for one set of data, but then the css can be changed to style the elements for a different set of data. I'm not sure whether this requires javascript, or if svg can handle it in the xml. </p>
  
  <p>thoughts?</p>