LOG4J2-763: Improved FormattedMessage, StringFormattedMessage, LocalizedMessage, MessageFormatMessage and ObjectMessage for asynchronous logging to ensure the formatted message does not change even if parameters are modified by the application. Improved docs for MapMessage and StructuredDataMessage. Improved site docs.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1617051 13f79535-47bb-0310-9956-ffa450edef68
LOG4J2-769 Startup takes a long time if you have empty packages attribute.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1617053 13f79535-47bb-0310-9956-ffa450edef68
LOG4J2-763 give credit

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1617054 13f79535-47bb-0310-9956-ffa450edef68