Add more tests, make toolbox.py Python2 compatible

The tests in tests.md are now separated into individual calls, rather than all glommed into one call. This makes it easy to see when something goes wrong, but it will eventually also be useful to test multiple marker-text pairs in one call.

toolbox.py is made to load with Python2 (there were only trivial things blocking it from loading), but no guarantees are made about its ability to run without error.