rename Pychrm to wndcharm

cc: @manics @igg

We have made the decision to drop the name "pychrm" for the WND-CHARM Python API and just call it "wndcharm".

In this PR, the build system is changed such that in python you would `import wndcharm` instead of `import pychrm`. In addition, the three Pychrm unit tests have been refactored to use the Python `unittest` framework. Running `python -m unittest discover` in the `tests/pywndcharm_tests` directory yields no errors.