When writing unit tests for XML data, it is more convenient to compare
list of lines, instead of a single string without newlines.
This helps identifying which lines in the diff printed on the console
don't match the expected result.
So, getXML now returns a list of lines,
To allow passing the same list of lines to the complementary parseXML
function in the roundtrip tests, parseXML now also accepts a list of
strings, as well as a single string.
We also use unicode_literals, and ensure that if the test modules passes
unicode str, we first encode to UTF-8 before passing on to expat XML
parser. This is because on Python 2, expat only accepts bytes strings.
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