Add testing setup

[ronen]

This PR adds a pytest setup; it's what I've been using while doing the refactoring.

Quick notes:

• Presumes you've installed pytest. Execute tests by running py.test
• Not (yet?) a fleshed-out test suite. Just some simple acceptance/regression tests to verify that the transcribers seem to work and do what they did before on the given inputs. No reason to think that it's exercised all interesting cases. But of course more tests could be added (especially TDD-style for future work).
• Test input data is in tests/data/inputs/... and result data for regression testing is in tests/data/results/...
• The full transcription results are likely to be somewhat platform specific at least in floating-point number values, and possibly even in the exact phonemes found. So probably the regression tests in this PR will fail for anybody other than me! Which means the tests should be changed from requiring exact equality to verifying for some higher-level correctness.