Add support for OpenFlags and vfs parameter to deadpool-sqlite

[bikeshedder]

See:

• https://docs.rs/rusqlite/latest/rusqlite/struct.Connection.html#method.open_with_flags
• https://docs.rs/rusqlite/latest/rusqlite/struct.Connection.html#method.open_with_flags_and_vfs

[jessekrubin]

how involved do you ( @bikeshedder ) think is this? I could take a crack at it if not super involved and I find some time

[bikeshedder]

I think it should be fairly simple. All that needs to be done is adding it to the configuration structure as Options and call the appropriate method upon construction of the manager.

[jessekrubin]

like this? #292