This function should only be used for testing purposes.

* Multiple calls to InitializeLogging can be made if desired; the first call * will initialize the logger as a singleton and subsequent calls will return * the same Logger instance.

stdout and stderr are passed in to this function to enable output redirection in tests.

* The following constants representing the current logging level, and are * cumulative (that is, setting the log level to Debug will print all Error-, * Info-, and Verbose-level messages in addition to Debug-level messages).

* Leveled logging output functions using the above log levels are implemented * below.