Tests are missing

[susnak]

As we move more code from Matlab to C, we have to ensure it behaves the same. We also need a way how to test the error checking and how to detect memory leaks.

• [x] Use the loadlibrary function from Matlab to test the correctness of the results against the pure Matlab implementation.
• [ ] Use CFFI from Python to make more tests.
• [ ] Make small test executables in C or C++ and test the correct memory handling using Valgrind or Google sanitizers (-fsanitize=* compiler option).