1.8.0 release

• TWEAK: The class constructor has a new signature. See UPGRADING.MD for all details; but, the fourth parameter (which you may not have used) is now an array for specifying options, and further parameters are abolished. A new parameter, require_login, has been introduced. It defaults in 1.8.0 to true (retaining the previous behaviour), but may change in future, so set it if you have a preference. If false, then updates checks will be made even if no credentials have (yet) been provided. This will enable showing updates information (but not actual updating) even when people have not authenticated, which may motivate them to authenticate.