Adds an appender to the logger
void addAppender( ple::simple_shared_ptr<Appender> appender );
A non-null pointer to a class descended from Appender If the level is set to LL_DEFAULT, then the severity level of the parent logger will be used. (Note that LL_DEFAULT may not be applied to the root logger.)
Messages sent to this logger which are of lower severity than the level set with this method will be discarded.
Messages sent to this logger which are of the same or higher severity than the level set with this method will be streamed to any appenders, and will be passed on to the parent logger.