add empty sessions controller and empty integration test
add basic tests and named route for /signin
add more session tests and initial view for /signin
create view for signin and update tests for sessions
add id to login form elements on sessions#new view
generate users controller
create view for users#new and move tests into users_controller_spec.rb
add logic for invalid sign-in, and place sign-up link below sessions form
write code to display flash messages on all pages in views/layouts/application.html.erb
add test and fix for flash message persisting too long
assign the user in the session when login is valid and create current_user method in sessionhelper
add show to users
add header partial and reconfigure named routes