Implement support for busy handler

I think it'd be good for these bindings to support https://www.sqlite.org/c3ref/busy_handler.html .

Use case: I'm currently writing an app that causes quite a bit of traffic to an SQLite database and am encountering contention. I wrote my own wrappers around the queries I'm issuing to handle SQLITE_BUSY errors and retry them... but I just discovered that SQLite3 has a built-in mechanism for this via sqlite3_busy_handler. It would be nice if we could register a hook via SQLiteConn or something like that.