add scenario - non logged in user attempts to create a ride
rename request_a_ride.feature to ride.feature
move request_a_ride_steps.rb to ride_steps.rb
generalize language in Feature section of ride.feature
add scenarios for non logged in user for edit and delete to ride.feature
ride validates presence of user_id
set ride.user to current_user in rides_controller#create
use current_user instead of @user (which is loaded from params) in users/rides controller for #create, #update, and destroy