add unit tests (issue #7)

This version introduces multiple enhancements:

added new part of tests and modified validation test

Details of additions/deletions below:
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Modified:   Test/ObjectTest.php
            -- Added --
                testAccessToDataByAttributes check access and setup data by object attributes
                testDisplayObjectAsString check echoing of object with separator changing
            -- Updated --
                testDataValidation moved at top of test and added checking validation by closures
                testAccessToDataAsArray added test for object single element