[Ur] New release

[Adam Chlipala]

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

CHANGELOG for this release:

- Improvements to type inference and error messages
- New Basis members: ceil, float, null, round, trunc
- New SQL expression forms: 'IF..THEN..ELSE', 'COALESCE', and 'LIKE'
- Support for the full set of HTML character entities
- Client-side versions of some time-related functions
- New URWEB_PG_CON environment variable
- Allow arguments for 'con' signature items, not just declarations
- Bug fixes and performance improvements
- Tweaks for idiosyncrasies of OS X (like deprecated OpenSSL)