Add size option to UsersHelper#gravatar_for
Refactor: Extract gravatar url parameters string building to module GravatarUrlParameters
Refator: creates gravatar url in one line
Add samples to user pages spec to test validation errors
Add key to label attribute user#password_digest to show a friendly name
Add sample to user page spec to test after save scenario
Display fash message in application.html.erb using the content_tag helper