LOG4J2-723 Clarified docs that slf4j API jar is required when using log4j-slf4j-impl.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1616232 13f79535-47bb-0310-9956-ffa450edef68
LOG4J2-722 Clarified docs that Commons Logging API jar is required when using log4j-jcl.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1616234 13f79535-47bb-0310-9956-ffa450edef68
fix: Commons Logging API jar -> Commons Logging jar

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1616235 13f79535-47bb-0310-9956-ffa450edef68
LOG4J2-765 Improve warning message if log4j-core jar not in classpath

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1616246 13f79535-47bb-0310-9956-ffa450edef68
LOG4J2-729 Emit warning message to console if no configuration file found.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1616252 13f79535-47bb-0310-9956-ffa450edef68