Update to RSpec 3
Expand Ruby and Rails version support
Specify the table engine for Arel
Handle psych/syck whitespace differences in spec
Remove note about Heroku mailing list
Don't double ActiveRecord::Base in specs

The method stubs can be used on the real object instead.
Add basic integration test using real ActiveRecord
Update RSpec configuration

* Use spec_helper.rb instead of base.rb
* Update spec_helper based on `rspec --init`
* Add a root-level .rspec file
* Remove explicit helper requires
Disable RSpec monkey-patching