[Ur] New release

[Adam Chlipala]

Available as usual at: http://www.impredicative.com/ur/

CHANGELOG for this release:

- Automatic insertion of implicit arguments in more positions
- Reifying expressions as URLs and redirecting to them explicitly
- More syntactic sugar for SQL
- Typing of SQL queries no longer exposes which tables were used in 
joins but
   had none of their fields projected
- Tasks
- Dynamic linking of the runtime system
- Optimization improvements
- Bug fixes