[Ur] New release

[Adam Chlipala]

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

CHANGELOG for this release:

- Changed URL escaping convention, to avoid confusing proxies.
   The new convention is like the normal one, but with '.' instead of '%'.
- Changed JavaScript compilation of recursive functions to use thunks.
   This change avoids most costs of functions not referenced on particular
   pages, reducing loading time dramatically.
- Support HTTP caching of application-specific JavaScript code
- Bug fixes