This is the module that I crafted together to add reStructuredText support to our Roundup instance: rounduprest.py. It's based on the rst2ht work by Ollie Rutherfurd, particularly the hthtml.py module. I added in Roundup Designator detection which turns Roundup references (ie - text like issue44) into Hyperlinks.
Update: Now rounduprest.py can take in an argument of 'roundup_class_names' that can be used to differentiate Roundup designators from regular text that happens to match the expression ('issue42' versus 'v2')