Fill color is still the same with 'color' (i.e. can be overridden by markup still), but now there's a stroke_width and a stroke_color option that, when stroke_width > 0, will draw an outline below the text. Since this isn't a Pango feature, we can't do markup for outlines. (Maybe make that a feature request to Pango if you want it.)
Implements #51
Andy Meneely