Rails 4 Support and Travis Integration

This PR:

i) Make attr_accessible inclusion conditional on ActiveRecord version, and doesn't include those in the models for Rails 4 and higher
ii) Updates the specs to eliminate deprecations
iii) Changes the specs to use modern FactoryGirl syntax
iv) Changed the default Rake task to use the built-in RSpec task
v) Added a .travis.yml that tests against MRI Rubies and Rails versions