Add option to make `using` a required argument

[meshy]

The original private form of this library always made using a required argument, but that was removed when making it public, because it is too much boilerplate for single-DB codebases.

Multi-DB codebases could benefit from being explicit about which database they're talking to, however. At the moment, they'll need to define their own wrappers of our functions to add that constraint. Is there some nice way we could provide that functionality optionally?...

[LilyFirefly]

We could add a new module, strict, that contains the strict variants. To avoid code duplication, we would probably implement strict as wrappers around the non-strict versions (or vice-versa).