Added an additional method OutputWriter.println(String, OutputListener, boolean) that accepts additional boolean parameter (is Important or not). It allows the API users to mark the line and it's listener as important. Such a line can be marked in different color, the output can stop there to draw user's attention etc.

The method should be ideally abstract but because it's uncertain how many implementations are there, the method is non-abstract and in it's default impl, delegates to the OutputWriter.println(String, OutputListener) method, ignoring the boolean parameter. Implementors of the class are encourages to implement the new method.