fixed text advance tracking to work correctly w/in a single line
ensured line breaks happen for cost symbols (not just text), but that runs of cost symbols are never broken to wrap across lines
added a little padding between the casting cost and the card title's bounding box
pulled all the variables for drawing the texbox into a DrawCtx type so that the implementation of drawing a given Renderable can be handed out to the Renderable itself, rather than doing type-check-based branching in the compositor (ick!).