Fix comparison to return -1, 0, 1 and Improve xml element content comparison

[bsrouji]

Fix comparison to respect -1, 0 or 1 return value, we can't assume returning 1 if col1 is lower than col2
Also improved comparison so when xml element have the same name and the same attributes, we shall then compare based on the xml content
for example:

<tests>
<test>2</test>
<test>1</test>
</tests>

should sort to:
<tests>
<test>1</test>
<test>2</test>
</tests>

[bsrouji]

I had to redo the fix and enable unit test that use your test_files
I also added a new h test case file
be aware I changed some of your _sorted files as with the new algorythm is sorting the innterxml when xmlelement and attributes are matching, also as we respect the return code (-1, 0, 1)

[kosi2801]

This improvement would be very appreciated. Is there any chance that this will be merged in the foreseeable future?
Or are there any parts missing or other reasons that require an improvement of this PR?