KmlDocument's version and attributes handling

[NikBel3476]

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Today i tried to use this library and notice that i cannot get document version, so I suggest these changes to fix it. I also provide the attributes to the document for passing the tests

[pjsier]

Thanks for this! Could you add a quick test to verify functionality? Then I think this is good to go

[NikBel3476]

Sure, I just added one

[pjsier]

This looks great! Thanks for adding that test