Added get/setElements methods, and javadoc updates.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1521848 13f79535-47bb-0310-9956-ffa450edef68
Ported Matrix4.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK7@1521849 13f79535-47bb-0310-9956-ffa450edef68