The test will try to match each XML file in input directory with
the file of the same name in the output directory.
It is possible to test lossy conversion as well (say legacy ezxml).
To use this file name of the fixture that is converted with data loss
needs to end with .lossy.xml. As input test with this fixture will
be skipped, but as output fixture it will be matched to the input
fixture file of the same name but without .lossy part.
Comments in fixtures are removed before conversion, so be free to use
comments inside fixtures for documentation as needed.
