Error - collect and report layered errors

Member functions in this class are used to store error messages, along with information about generic type and severity, format error messages into a form suitable for display to an end user, or marshal them into a form suitable for transferring over a network.

Error objects are used to collect information about errors that occur while running a Helix Server command.

When a connection is opened with ClientApi::Init(), a reference to an Error object is passed as an argument to Init(). This Error object then accumulates any errors that occur; a single Error object can hold information about multiple errors. The Error can then be checked, and its contents reported if necessary.

Although Error itself does not provide any virtual methods that can be re-implemented, the manner in which errors are handled can be changed by re-implementing ClientUser::HandleError(). The default behavior for handling errors typically consists of simply formatting and displaying the messages, but Error objects maintain additional information, such as severity levels, which can be used to handle errors more intelligently.