Create "standalone" examples

[alaindargelas]

@hzeller, moving original tests (Running with Makefile and with a main function) to Google tests with Cmake has made them harder to grasp for the people not familiar with Cmake and Google tests.
See: #782 (comment)

We need simpler examples with a simple Makefile.

[hzeller]

the Unittests are more to test the APIs on the low-level, so that is more for us whenever we implement internals and test things (the main function already comes for free as we link with the main that auto-detects the tests).

Google tests are one of the most common unit tests frameworks in that space so anyone doing C++ will/should be familiar with it.
Currently we're using cmake, which is annoying but should also be fairly common.

For use-cases to get started with the API, I think this is where hellodesign.cpp , hellosureworld.cpp, and hellouhdm.cpp are better suited. They come with their full main function and show an end-to-end example.