I'd screwed that up. Also, fix some bugs in the #to_md output method. Still not correct (and I'm not sure I'm going to bother completing the job), but better.
Image titles were not being output (a long-standing Maruku bug). Also fix some broken specs. All the HTML specs pass. I hope they're "correct".
Modify Maruku to use Nokogiri instead of REXML. Produces a 3-fold speedup in the #to_html method.