[Ur] New release

[Adam Chlipala]

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

CHANGELOG for this release:

- Parsing extension: monadic bind supports patterns, like "(x, y) <- a; b"
- New, optional less safe FFI
- New HTML tags: <tbody>, <tfoot>, <thead>
- HTML5 data-* attributes
- HTML5 semantic tags
- Syntactic sugar extension: allow parens grouping joins in FROM clauses
- Bug fixes and documentation improvements