Add omniauth-facebook gem
Add provider & uid to users table
Add configuration and credentials
Make User model devise :omniauthable
Add 'sign in with FB' link
Route devise routes to omniauth_callbacks controller
Add OmniauthCallbacksController
Remove uniqueness constraint on username
Add methods to create new user & new session on User model
Merge pull request #3 from hchood/add-omniauth

Add omniauth