Add sessions controller and login form
Add log_in helper,invalid login test and Create action
Add current_user helper
Add layout links to _header.html
current_user correction
app controller correction
_header correction
Add test valid login information , fixtures,User.digest method[password for fixtures]
Add login upon signup[create,signup test,is_logged_in helper]
Add log_out helper, destroy action and update login test[for log out]
Add remember_digest migration,new_token,remember(user.rb),authenticated?,remember(sessionshelper) and update current_user
Add Remember me[session/new,css, update controller-create]
Add forget user(user.rb,sessionhelper)
Add bug-fix for logout in second tab and second browser
Add test for remember branch[sessions_helper_test]