Wrap sqlite3 OPEN_URI option

[BurningEnlightenment]

Add a boolean option to the Database constructor controlling the SQLITE_OPEN_URI flag. Obviously this isn't a superset of #735, but it implements its most requested feature.

I'm open to bikeshedding w.r.t. the option name.

Please note that I disabled the directory existance check if uriPath is passed. If the URI requests that a custom sqlite VFS implementation is used, the db path might not be accessible by the node fs APIs. Furthermore an extension can install itself as the default VFS, so it might make sense to completely remove that check. (Also note that it generally suffers from TOCTUO issues -- the directory can be deleted after fs.existsSync() succeeded but before sqlite3_open_v2() tries to open the file).

Closes #483

[mceachen]

Nice! Can you add some tests please?

[BurningEnlightenment]

Can you add some tests please?

I added a smoke test for the new option. Is that sufficient?

[BurningEnlightenment]

Closing due to lack of activity / interest.