Add code to generate downloads/index.html

Unfortunately I don't have access to the machine containing the download database right now, so I can't provide a real `download.json` now. I'll provide a real download.json ASAP, but that'll probably have to wait until next weekend. 
Looks good, only thing missing is error handling. ie ``scope(failure)``.  Should probably have some custom error handler, but not needed for the moment.