renamed SetIconFactory to CardSetIconFactory for consistency with CardSet
redocumented the artwork to say it'll be scaled to cover, not scaled to fit.
 * removed SpellCard and LandCard, as they're not interestingly differentiated for constructing cards, even though they make a difference in gameplay
 * fixed a couple names/docs in levelers and planeswalkers for consistency
added note about null level start being silly
added a 'descriptor' module for housing cardset descriptors
started working on a XSD for cardsets