Merge pull request #27 from kimrgrey/master

Url helpers were namespaced.
Update bundle
:wave: to demo app, say hi to the live demo on heroku
Update CHANGELOG
Upgrade to rspec 3
Convert specs to RSpec 3.0.1 syntax with Transpec

This conversion is done by Transpec 2.2.4 with the following command:
    transpec

* 4 conversions
    from: obj.stub(:message => value)
      to: allow(obj).to receive_messages(:message => value)

* 2 conversions
    from: =~ /pattern/
      to: match(/pattern/)

* 2 conversions
    from: it { should ... }
      to: it { is_expected.to ... }

For more details: https://github.com/yujinakayama/transpec#supported-conversions
v1.2.1
Added validation of params for letters_controller.