Add unit tests infrastructure

[gguedesaz]

What do you think of adding an Unit tests infrastructure?

Currently, the tests in Tests/main.cpp have no explicit checks (I guess you look at the results "by eye"). If there is an unit tests infra, it would be way easier for developers to check they didn't mess up with an already working algorithm, add new test cases, etc...

We could use google tests to do it (https://github.com/google/googletest). The good news is that the licenses are compatible.

@sudz123 , please let me know if you like the idea.

[gguedesaz]

Of course, if you agree with the idea, I'll be glad to implement it.