Okay, I'll send a pull request.

Adding MySQL support would be pretty tricky, I think. To emulate certain operations on sorted sets, I ended up just pulling the fully data set and processing it in JavaScript. Since SQLite is in-process, that's not a huge issue. You can't really do the same with a real RDBMS. The expectation level is different too. If you're choosing SQLite as a storage mechanism, you know you're sacrificing scalability for the sake of a reduction in hardware requirement.