Update to SQLite 3.8.4.1

The newest versions of SQLite have added support for [recursive comment table expressions](http://sqlite.org/lang_with.html). These allow making recursive queries with SQLite and are *extraordinarily* useful. I'm very excited about having these available with `direct-sqlite`!

That's my main motivation for this PR, although there have of course been a number of other performance enhancements and new features between SQLite 3.8.1 and 3.8.4.1.