Add support for running commands before hardcoded pragmas

I tried building this project with sqlcipher, but it fails because the pragma key = '...' needs to be the first command after opening the database (if it's encrypted of course).

The issue is that the SQLiteDriver.Open() issues various pragmas before letting the client code. This could either be fixed by adding support for a new _pragma_key parameter or adding support for running arbitrary pragmas before the first PRAGMA busy_timeout = %d; runs.