Add unit_helper for Unit testing
Add Person
Add virtus gem and `bundle install`
Modify Person to include Virtus and remove AssignAttribute
Create a Thing class
Clean up Gemfile a little and `bundle install`
Change Thing attributes

Things should have an :id.
Things should have a :name.
Things may have a :description.
Modify Person

Person should have an :id.
Create a Loan
Create a User
Add integration_helper.rb

Integration specs need their own helper.

Also, neither Unit nor Integration specs need to require files in the 'lib'
directory.
Refactor Loan

Loan absolutely must have a Thing association.

loan.rb should specify its class dependencies (i.e., Thing and Person) via
require statements. Also, I should be using `require_relative` instead of all the `../../etc.`
syntax in these requirements.
Add loans collection attribute to Person

I had to add lazy-finalization to Virtus configuration to make this work.

Also, somehow I forgot to add an :id attribute to Person, so that is included
in this change as well.
Refactor User

The User and Person models both had an email address. Because (as of now) there
is a one-for-one relationship between the two, I decided to implement a :person
attribute on User, and moved the :email attribute to Person.
Add `Virtus.finalize` in unit_helper.rb

Virtus needs lazy-finalization to handle circular dependencies (i.e.,
Associations)
Add #lend and #borrow to Person

The :loans attribute belongs to Person, and Person should manage its own Loans.
Add a Creating a Loan integration spec

Implement a #lend and #borrow method on User.
Create integration_helper.rb
Implement the specs.
Merge branch 'create_some_domain_models'

* create_some_domain_models:
  Add a Creating a Loan integration spec
  Add #lend and #borrow to Person
  Add `Virtus.finalize` in unit_helper.rb
  Refactor User
  Add loans collection attribute to Person
  Refactor Loan
  Add integration_helper.rb
  Create a User
  Create a Loan
  Modify Person
  Change Thing attributes
  Clean up Gemfile a little and `bundle install`
  Create a Thing class
  Modify Person to include Virtus and remove AssignAttribute
  Add virtus gem and `bundle install`
  Add Person
  Add unit_helper for Unit testing