add unit tests (issue #7)

This version introduces multiple enhancements:

fixed tests for simple xml data

Details of additions/deletions below:
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Modified:   Test/ObjectTest.php
            -- Added --
                _convertType allow to convert arrays or boolean information to string
            -- Updated --
                testCreationSimpleXml launch type convert before assertion
                _exampleSimpleXmlData launch type convert before insert data into xml