Hi Cédric:

Is this patch supposed to create links for emails as well?

+        for group in ['url', 'email']:
+            if match.group(group):

If so the patch is missing the email test cases.

(I am still mystified what this code does and how it works.
Is it just taking some random re/match and looking for a named group?
Then it uses the presence of the group to determine what was matched?)

Also I had to modify the tests a bit. Markdown doesn't include a 
trailing \n on the rendered lines, so I am using m.rstrip('\n') and
removing the trailing \n. Also where you have self.assertIn I added:

 '<p><img alt="" src="http://example.com/" /></p>',

for markdown (apparently it sorts attributes by name).

Agreed on setting rel on the links. That should be a new ticket most
likely. Also looks like I need some doc added for markdown.
Explain settings, url rendering, differences from classic text
rendering (lack of rel=nofollow) etc.