Remove growl from development dependencies
Add specs for SignedRequest middleware
Add specs for RaiseErrors middleware and fix typo in #unsuccessful?
Add specs for RaiseErrors middleware and define API error classes
Configure VCR and specify test user in ENV variable
Add specs for Client authorization methods
Add specs for Client#deorbit and Client#deauthorize
Prepare integration tests for CI

* Use Travis CI secure environment variables
  (http://about.travis-ci.org/docs/user/build-configuration/#Secure-environment-variables)
* Skip specs marked `:external` when secure environment variables are
  not present.
Fix typo in config support file
Merge pull request #8 from gevans/refactor/code-coverage

Code coverage, more cleanup, etc.