Explore the use of multi-db connections to isolate reads from writes

Rails uses its multi-db feature to accelerate sqlite by having two connections, 1 for writes and 1 for reads. To test this out we will need:

1. Load tests that combine read/writes. This is already underway.
2. Addition of a secondary db connection when `database()` is called via `apsw.Database.attach` called something like "read_DBNAME"
3. Modify read methods to access the `read_DBNAME` connection

Note: I put this in apswutils rather than fastlite, as a lot of devs access apswutils read methods directly.