Updated CMakeLists.txt to enable coverage.
Updated instructions with howto for coverage and also a separate
set of instructions how to run during a TDD cycle with coverage.
* 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
