* Move "using namespace std;" from header to module file (to no longer pollute the global namespace).
* Fix inconsistency of having namespace prefix in test code.
* Add include guard to GildedRose.h.
* Avoid std::endl.
* Have consistent white-space.
* Make it possible to build and run tests in CLion
and Visual Studio 2019 out of the box
* Provide four types of initial test using different test frameworks:
* Catch2 test framework
* Traditional unit testing using Catch2
* Approval test using Catch2
* Google Test test framework
* Traditional unit testing using Google Test
* Approval test using Google Test
* The different types of initial test are located in separate folders
in the test folder.
* Remove scripts to build and run tests and replace
with instructions in the cpp README.md
* Use C++17
* Use CMake => 3.13
