title: sl4j loggback configuration for same logger to two different appender with different levels
body: <p>How to configure the loggback in SL4J?
  My project has many classes: class1, class2, class3...
  I want to do this two things:
  Log all classes to a file appender named FILE1 with WARN level (class1, class2, class3...)
  Log one class named class1 to a file appender named FILE2 with DEBUG level.</p>
  
  <p>The trouble is that when I configure the logger for class1 to FILE1 appender with WARN level I don't know how to configure the same logger (class1) to FILE2 appender with a different level (in this case DEBUG).
  I can configure both appenders to the same class but not with different levels.</p>