Wrap up initial development.

When I last worked on this plugin I had sketched out it's basic structure
but it was all just un-executed code spikes to determine to pieces.

Since that time Daniel Honig had started on adjusting my basic structure
to use a 3rd party Smarty Streets gem for the API integration. Although the
API interaction was trivial using a gem was a better decision as it gives
access to richer data should this plugin continue to be enhanced.

This commit continues that work by transforming a sketched out basic structure
into working tested source code. Changes made:

* I got rid of my old module that I had planned to use to implement the API
  interaction (app/models/concern/smarty_streets_address_verification.rb).
* I got rid of what I believe was just some example tested code that Daniel
  had imported (spec/address_verifier_spec.rb and lib/AddressVerifier.rb).
* I got rid of the module that Daniel was working on that I believe was trying
  to merge what I was trying to do with my module and what the example code
  was trying to do. I don't think this module is necessary. The only reason
  I had created a module was to abstract the API interaction. Since the 3rd
  party gem is doing that for us I believe we can just put everything in the
  decorator and keep the code simpler.
* I moved the environment configuration out of the check and into the loading
  process. This way if an application doesn't have the environment variables
  set it will error earlier.

There are a few other minor bits of cleanup:

* When Daniel imported my rough draft I had accidently left a file created
  by my editor (.zedstate).
* I included dotenv into the test process to ease setting the environment
  variables during testing.
* I updated the README file to be more current.
Remove unnecessary testing support.

The base of this extension was generated by Spree's generator. It provides
a boatload of testing support to do testing at all levels of the stack.

Since this extension just decorates at the model level much of that support
is unncessary and slows down the testing process. This commit removes that
unnecessary support leaving just the testing facilities we are using.
Add test to ensure connectivity or configuration errors bubble up.

About to call this addon completed when I noticed rcov indicating I failed
to write a test for the case where a general connectivity or configuration
error has occurred.

We are just wanting to bubble that error up so the ops team can detect the
issue and resolve it. This tests verifies this so we know we are not swallowing
the error.
Merge pull request #1 from railsdog/working-code

Initial Working Version