LOG4J2-654: added log4j-perf module with support for JMH microbenchmark performance tests

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597422 13f79535-47bb-0310-9956-ffa450edef68
added target directory and IDE files to svn ignore

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597423 13f79535-47bb-0310-9956-ffa450edef68
added instructions on how to run this microbenchmark

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597424 13f79535-47bb-0310-9956-ffa450edef68