Usage updates

This has a bunch of updates from me actually going and using the CLI with a Postgres database configuration.  The commits kinda tell the story, but here is a rundown:

* I first went and created some dirs under tmp/ for manually running the CLI against pg, sqlite, and mysql configurations
* then using this setup, I went and made a pg db.rb and Gemfile and starting running the CLI against this
* I needed to update how the configs were validated and I made the CLI expect config/db.rb so I could load in my configuration
* the last two commits are all about fixing things that broke when running the commands and improving the error handling and reporting

@jcredding this is ready for review.  For some context, the next step is getting a sqlite implementation going so that I can write some actual system tests for all this.  Then I can move on to other things like the mysql implementation and helpers.