execute JSON-encoded regression tests against multiple backends

This is looking much better after the third re-write or so. Now using Argonaut's DecodeJson and a RegressionTest case class to encapsulate loading the JSON tests, and using Tasks in a fairly disciplined way to encapsulate/chain the effects of setup, query, and verifying results.
Maybe instead of having this println, runQuery can return the log at various stages? i.e. push this decision up to the top.