Make it possible to use alternative sqlite3 drivers

[Alexey Palazhchenko]

For example, there is https://modernc.org/sqlite – a transpiled version of sqlite3 into Go.

I think it would be better to make both drivers optional and make users import the right one instead of importing both github.com/mattn/go-sqlite3 and modernc.org/sqlite.

[Piotr Jastrzębski]

#13 switched to modernc.org/sqlite