Completed the exercises in Chapt. 5
Added bcrypt gem and bundled
Added user, email index and password digest migrations
Added validation for name, email, password. Including presence, length, format and uniqueness
Created User Unit tests
  Using TDD we added tests for all the validations of the user attributes:
    - name: presence, length
    - email: presence, length, format, uniqueness
    - password: length
  Added callback to save emails in lowercase format
Updated schema