Allow the RepositorySelector type to be sepecified using the AppSettings config.
The RepositorySelector is set by default to be DefaultRepositorySelector. This can be changed programatically by setting the LoggerManager.RepositorySelector property, however it cannot be set at runtime via the application configuration files.
Propose adding an AppSettings property 'log4net.RepositorySelector' that can be set to the type name of the repository selector to load. If this property is missing, or the type cannot be created the current default behaviour will continue.