PROTON-256: Improve Javadoc

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1453851 13f79535-47bb-0310-9956-ffa450edef68
PROTON-257: Added test that illustrates use of the Engine and Message proton-j APIs. Also added LoggingProtocolTracer and TestLoggingHelper. Configured Java Logging during test runs initiated by Maven.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1453852 13f79535-47bb-0310-9956-ffa450edef68