Add validation to User model
-write validation test
Add email validation
-add test for email validation
Add failing test for user name length validation
Add length validation for user name
Add failing test for email format validation
Change email to a valid email address
-email format validation tests are green
Add test for email uniqueness
Add unique index on user email attribute
-add before_save callback to downcase user email
Add migration to add password_digest attribute to users table
-add bcrypt gem