add unit tests (xml data) (issue #7)

This version introduces multiple enhancements:

test creation object with xml (also with attributes)

Details of additions/deletions below:
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Modified:   Test/ObjectTest.php
            -- Added --
                testCreationWithXml allow to create object with given xml data
            -- Updated --
                testCreationSimpleXml renamed to testCreationWithSimpleXml
                _exampleXmlData moved upper and added logic to create xml data