Tests for mathematics

[bertfrees]

Math is out of scope for now, but of course priorities may be shifted if the necessary resources are found. We can start with writing the tests, and based on those tests estimate the amount of work needed. For the tests for Dutch braille, test_translate-mathml_woluwe.xprocspec can be used as a starting point (assuming the Woluwe code is still the code used in the Netherlands).