Adding Devise 3.1.x to Gemfile

The `gem "devise", "~> 3.1.0"` declaration indicates that I only want
to use versions of Devise that are in the 3.1.x family.
I believe Devise is using to [semantic versioning](http://semver.org/)

Devise is a "Flexible authentication solution for Rails with Warden."
https://github.com/plataformatec/devise

Warden is a "General Rack Authentication Framework"
https://github.com/hassox/warden

Rack is "a modular Ruby webserver interface"
https://github.com/rack/rack
http://rack.github.io/
Bundling up Devise and its dependencies.

Among other things, Devise added the following dependencies to our
project.
    devise (3.1.0)
      bcrypt-ruby (~> 3.0)
      orm_adapter (~> 0.1)
      railties (>= 3.2.6, < 5)
      thread_safe (~> 0.1)
      warden (~> 1.2.3)

The following commands were run:
$ bundle
Adding rspec-rails as a :test group dependency

Project Hydra traditionally makes use of the Rspec testing framework.

From http://rspec.info/
RSpec is testing tool for the Ruby programming language. Born under
the banner of Behaviour-Driven Development, it is designed to make
Test-Driven Development a productive and enjoyable experience with
features like:

* a rich command line program (the rspec command)
* textual descriptions of examples and groups (rspec-core)
* flexible and customizable reporting
* extensible expectation language (rspec-expectations)
* built-in mocking/stubbing framework (rspec-mocks)

By declaring rspec-rails in the :test group, the gem is only available
when the application is running in test.
Bundling up rspec-rails and its dependencies.

The following commands were run:
$ bundle
Initializing rspec for our application

The following commands were run:
$ rspec --init
Setting test framework generator to rspec

By default Rails provides numerous generators. Other gems can also
provide generators. Run `rails generate` or its synonym `rails g` to
see a list of all the generators.

Most generators will generate "production" code and "test" code. By
setting our test framework to :rspec, the generators will – if they
are written "properly" – create rspec files for us.

http://guides.rubyonrails.org/generators.html#customizing-your-workflow
Generating devise user

The following commands were run:
$ rails generate devise User