Add a User model
Add a schema.rb

Created by a command 'bundle exec rake db:migrate'
Add a test for :name and :email
Add a presence and length validation
Add a email format validation
Add a test for email uniqueness
Enforce email uniqueness
Update Gemfile
Add a password_digest cloumn to users table
User authentication using has_secure_password
To avoid deprecated message
Merge pull request #3 from takatoshiono/modeling-users

Chapter 6. Modeling users