Database adapters in Biff 2

I've released two new Biff libraries, both database adapters: biff.sqlite and biff.xtdb . Both of them implement some interfaces used by various other Biff libraries, and they also both implement additional functionality that can be useful to Clojure apps even if they aren't using Biff. The interfaces So far, modifying a Biff app to use a different database than the default has been kind of…