Allow looking url hashes up for badness

* Common logic between lookup and lookup_url_hashes
methods is extracted into private class methods.

* Variable renamed to increase readability of the overall code.
Don't load active_resource/railtie in dummy rails app

Rails 4.0 complains if the dummy app attempts to
load active_resource/railtie since it can not find that file.
However, Rails 3.x doesn't complain.
Document lookup_url_hashes method in readme
Bump gem version to 0.6.0.

Also, update Gemfile.lock with bundle update.