Update README.md
Update README.md
Specify Ruby 2.1.1
Generate Address model.
Add shoulda-matchers.
Street address validations.
Validations for city.
Validates states against fixed list.

50 states are included in lib/constants.rb, both full names and abbreviations.
Zip code validation: must be 5 numbers.
Merge branch 'addresses' into 1_create_contacts
Generate Phone model, by defaults numbers are not primary.
Validations for phone numbers.
Merge branch 'phone_numbers' into 1_create_contacts
Rename Phone to PhoneNumber

'phones' sounds odd.
Generate contact with name only.

Foreign keys added next for address, numbers.
Validations for first and last name.

Any alphabetical characters allowed
Both first and last name must be present.
Associate Contact with PhoneNumber

Foreign key `contact_id` is on phone_numbers

Contact has many PhoneNumbers
PhoneNumber belongs to Contact

Phone numbers cannot be created without associated Contacts.
Associate Address with Contact.

An Address can be shared between contacts, since many contacts can live in the
same household.

Address has_one Contact
Contact belongs_to Address
Fix factories to comply with validations.
Add foreign key constraints, dependent:destroy for phone numbers.