Explain service adaptor testing, include bX service adaptor test, fix fixtures

I updated the fixtures to not use ID since it was unnecessary.  All that noise about Travis parsing fixtures differently in the commit comments below is garbage.  It may be true, but it wasn't my issue.  I needed to include the `:referent_values` fixture in my test.  That was all.  

I've also included a unit testing README explaining how to test service adaptors.

And, of course, I've included a bX test (with VCR cassette) and fix.