Implement toString() for debugging.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1516686 13f79535-47bb-0310-9956-ffa450edef68
Format for 120 line length and clearer Javadoc.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1516687 13f79535-47bb-0310-9956-ffa450edef68