Add password_salt attribute to User.

Updates specs, controller (user_params), and views to reflect the new
attribute.
Update User model's password_hash attribute to password_digest

Modified are the migration, specs, controller, and views.
Add a sign up form utilising has_secure_password.

Adds bcrypt-ruby to the Gemfile, modifies the user _form, adds :password
to permitted parameters in the controller, adds validations in the model.
Removes several attributes from User.

password_salt, confirmation_code, and is_confirmed are gone.
Updates specs, views, controller, migration, and schema to reflect this.
Moving comments around
Fill in sign-up values for new Users
Route /sign_up to users#new
Add the result of rails g controller Sessions

Includes session logic and modified routes
Move application layout from old erb to our modified haml
Add simple flashes layout
Move log in form to one view only
Minor language changes
Fix haml bug
Add POST log_in route and fix a route typo
Re-render the log in form on an error
Remove username attribute from User

Updates specs, views, controller, migration, and schema to reflect this.
Add current_user to application controller
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