6.1 Add basic User model
* create model with rails generate model
* rake db:migrate
6.2 User Validations
* Add spec tests for User name and email validity
	* presence, format (email), uniqueness (email)
* Add validations to User model, including email REGEX for format
* Add email index to users, and enforce uniqueness on the index
6.3: Add secure password
* add bcrypt-ruby to Gemfile
* add migration to add password_digest field to User
* add specs to test for secure password properties
* add validations to user.rb for password length
* add has_secure_password to user.rb, which automatically adds password and password_confirmation attributes, and adds implementation of creating password_digest, and authenticate method
6.5 Exercises
* Add test for downcasing email before saving to database
* Update VALID_EMAIL_REGEX to not accept consecutive dots in an address
Misc - added spec and implementation for validating name > 2 characters long.
Merge tag 'ch6_modeling_users'