[Ur] New issue tracker

[Adam Chlipala]

There's a new issue tracker for Ur/Web, where you can report bugs and 
make feature requests.
    http://www.impredicative.com/mantis/

I'd ask anyone who has reported an issue that's not yet been addressed 
to please add it to that system.  Don't be shy about adding your feature 
requests, though of course I'm not promising anything about timelines 
for implementing them.