Give the possibility to configure level for future loggers at runtime

[toki07]

When setting the log level using SimpleLoggerFactory, it does not apply to loggers created after.
It is confusing, because we should firstly create a logger with a standard log level, to modify it afterwards.

For Exemple

public static void main(String[] args) {
   SimpleLoggerFactory factory = (SimpleLoggerFactory) LoggerFactory.getILoggerFactory();
   factory.setLogLevel(Level.WARN);

   Logger logger = LoggerFactory.getLogger(some.class);
   logger.info("INFO LOGGED");

This log will be shown, but it shouldn't

[GoodforGod]

Version 1.0.0

[GoodforGod]

Behavior is identical to original slf4j implementation but I see your point